Lots of happy AE300 owners on this forum, myself included (though I too am a relative newbie). I haven't seen the Hitachi, but it has a lower resolution panel than the Panny and is definitely an entry level PJ, albeit one with "this year's technology". The Panny is arguably one step above it on the ladder, but uses "last year's technology".
Unfortunately though, you cannot mount the Panny on a high shelf near the ceiling, unless it is upside down (why not bolt it underneath the shelf?) Assuming the PJ is sitting the right way up on a shelf or desk, the bottom of the image is roughly level with the lens and cannot be adjusted. As I'm sure you are aware, the Hitachi has a lens-shift function (and a very flexible zoom as well).
Final point - don't go by magazine reviews. Demo if you can and let your own eyes decide. I can point you to some utter rubbish in hifi and home cinema magazines. IMO, the views and opinions on this forum and in its US counterpart over at avsforum are much more reliable.
I have my AE300 mounted on a high shelf upside down with 4x1cm foam pads that I had left over from some speakers lifting the PJ about 1cm off the shelf to aid airflow.
As for the Hitachi. How much is it? It has the same ansi brightness and contrast as the AE300 but has the same resolution panel as the old AE100. It doesn't have the smoothscreen technology of the AE300 which reduces screendoor. tbh it looks more comparable to the AE200. If its the same price as the 300 I'd go with the 300. If its cheaper well then your decision is harder.
Calibos.....Doesn't your exhaust port get blocked? I thought you need 2 feet space behind it?
I have a AE500 and was considering mounting mine onto a TV wall stand fixed on the rear wall (with the fan exhausting into the bay window), but alternatives would have the fan close to the wall as yours is...
The perspective in the pic is misleading. Heres another pic from a slightly different angle.
The back exhaust of the PJ is about 16 or 17 inches from the back wall. Recommended distance is 18inches. Close enough I'll let you do the math to figure out how deep that shelf is! Sounded horrifc on paper. Looked horrific before shelf was mounted. When it was mounted....."hey thats cool, it deflects some of the PJ noise away from the listening position, it kinda encloses you making the seating position more snug, its like sitting in the back row of the cinema under the projection booth etc etc"