Interesting dillema, especially with the Panny price drops. Howver, theres a lot to consider so the response is lengthy!.
The opions expressed are mine, and outline the various criteria I was looking at when spending £3-3.5k on a display. Your criteria may well be different.
I went through simalr decision, but with the Pioneer 433MXE and the Panny TH-42PHD (the 1024 x 768 native display), so was actually comparing two displays of same resolution.
Firstly resolution. With your decision I am sure youre aware that the Panny resolution is 840 x 480, the Pioneer is 1024x768.
Theorectically, the best way to view any source is to match it as closely as possible to the displays native resolution. What this means is watching a Region 1 DVD, the Panny resolution is exactly the same as source when run in progressive. Region 2 DVD's however will be downscaled to meet Panny resolution (576p for Region 2).
With the Pioneer everything will be upscaled, ie the 480p/576p, will be scaled to meet the 1024x768. Consequently, you will be watching all of the sources picture's intended lines of resolution, but be more dependant on the displays internal scalar.
TBH the difference this makes as far as I could see was negliable, simply because of the limited resolution of current DVD /TV sources.
However, if you plan on making this the centre peice of your set up for a few years, the additional resolution of the Pioneer is most definently a bonus, this will become increasingly important in my opinion, there is already a HD version of T2 available, this trend will become more common and more easily accessible with HD DVD players.
This future proofing criteria was the main reason I opted for the Pioneer. The Panny does not, indeed will not support HDCP DVI connectivity. Basically a copy protected digital connection which two large US studios insisted on manufacturers adhering to prior to allowing HD content to be available.
As more and more HD sources become available, whatever the resolution/capability of your display, you will not be able to view them as intended unless your display is equipped with DVI HDCP in the first instance.
But this is due to change again, the problem with DVI (among others) is its inability to support 576p as it is a PC signal, this has been addressed with the advent of HDMI, another copy prtotected digital signal with other advantages. Again Panasonic have no plans to intergrate this into their displays (only 6 series & above I beleive).
Pioneer have, on the other hand, licienced third parties to develop input boards for the MXE (Panasonic have not). Two of these are imminent the Aurora card and the Key Digital (based on HD Leeza).
So just in terms of protecting your investment, the Pioneer makes much more sense.
With PQ, I demonstrated both. TBH, out and out the Panny had far better blacks, this may be very important to you.
But, comparing the two side by side the Pioneer had better detail in darker scenes (due to its greater greyscale). The Pioneer also had better more natural colours (around 578 Million) than the Panny (16.7 Million) due to its greater range.
Also with the Panny that you are looking at (PW as opposed to HD), it uses single scanning technology Some users have complained about the flicker this causes on the display (the Panny HD does not).
Another minor issue for me with the Panny was its inability to have multiple video inputs at the same time, ie could not run S video and Composite together.
Another factor was the fact that Panasonic's Six series is imminent, I did not have the patience to wait, and did not really want to buy a display that would be superseeded in the near future, especially when to me it offered very little future proofing. The MXE is not being replaced for about a year.
So the only thing against the Pioneer to me was its black level, when compared to Panasonic, but this effect can be minimised by getting it calibrated by Gordon, as I did. You wont notice unless sat in a shop comparing the two displays side by side, not in my HT at home.
With respect to the ISCAN, im not in a posistion to advise, as not looked at it. But what I can tell you is that I recently demo a Lumagen scaler, running 720p, on my MXE - Whhhooa !. Honestly, my crappy Freeview RGB output was made to look like a PAL progressive DVD !. You can contact Joe from Media Factory re these.
Forgot to mentioned the Pioneer gives you an extra inch, 43 inch as opposed to 42 inch !
One other thing re the ISCAN, it will not scale beyond 567p, all it will be doing is it does the deintercaling/scaling as opposed to the display (pioneer or panny).
It guess it may have advantages on normal TV and DVD viewing. But I see you have an Arcam 88, have you upgraded its to support Progressive?, if so then you wont see any real benefit when watching DVD's through ISCAN.
In fact I am sure that both the Arcam upgrade (£350.00) and Iscan use Silicon Image 503 or 504 technology.
How much is the ISCAN these days? (approx £500.00?).
The reason I ask is now youre going for Pioneer (best decision IMO), theres a couple of things youll need to be aware of.
You will have to buy the PD-5002 Video Board, most dealers will include this but as an additional cost (approx. £250.00 I think) thats hidden in over all price.
The Lumagen Vision scaler (www.lumagen.com) can be purchased from Joe at the Media Factory for around £1.1k I think. However, with this you will not need the PD - 5002 Video Board, all inputs can go via the scaler. Joe will then deduct the price of of the Video Board from the display. Couple this with the additional cost you would have paid for the ISCAN, which is just a deinterlacer, then the two solutions will be fairly evenly priced.
Simaler price for the solutions, which one will give you the best for your money?. Thats a no brainer !!.
Just consider the Lumagen will provide excellent per pixel deinterlacing, far better than the display/ISCAN, not only that but will then scale the source in the best manner possible (whether from 480p/576p/480i/625i) to a maximum of 720p or 1080i (and to 1080p!) - ie true high definition resolutions for a high definition display. I honestly think that there is currently no better way at the price to view your pending Pioneer 433-MXE, or indeed any other HD display.
I really recommend talking to Joe from Media Factory, I found him an invaluable source of info and assistance (www.tmfsolutions.co.uk)
Just to add we used 768P at Tony's for the short demo of Vision.
Dealers who sell Lumagen product are required to carry a demo unit. This is for two purposes. They get to understand the product and how it works and it allows them to "demo" it with clients on their specific displays in order to ensure compatability. I like to think that the dealers I have on board just now are not likely to stitch folk up for a few bob.....