Hi jaffa,
What a loaded question. Lol. I love it, so where to begin.
Obviously rbe doesn't affect you or you see very little so it's a non issue. Like me. I loved the sharpness and film quality of my hd20.
So let's deal with your questions one at a time and my thoughts.
Q/1. Throw distance 4m, nearly same as mine. (I'm 4.5m)
A/1. Good distance, long throw. Projector behind you so noise not an issue. I watch from just under 3m.
Q/2. 120" screen.
A/2. Great screen size. To balance image size with brightness and sharpness on 1080p.
Q/3. Lens shift, motorised or manual.
A/3. Nothing beats a considered and careful installation of your projector. When I installed my hd20 which didn't have lens shift or great optical zoom. I think it was 1.1 or 1.2. It had keystone correction. After calculating distance ceiling mounted the projector then using tape measure and laser leveller fitted screen exactly square to the lens. Never needed to adjust in 6 years with good conformity over the whole image and no need for any image quality reducing adjustments. I only used a 16:9 screen and never changed the aspect so motorised lens shift would have been wasted on me.
Q/4. Epson 7300.
A/4. Well, I think this is a transitional product along with the 9300. The technology is still based on a full hd image with pixel shift to create extra perceived resolution/detail/sharpness. This way of quasi 4K is used by JVC also with their great blacks. Though wasted if you don't have a bat cave.
Q/5. The new (quasi) 4K Optoma.
A/5. Yes, it doesn't have the lens options, or even perhaps the quality of lens optics of the epsons and definitely of the JVC's. Nor does it have 3D. What it does have is, in my opinion, a much better solution for 4K than the Epsons and JVC's. There is a very animated discussion in this forum relating to exactly this. I'll find the link and post it for you to read. The image from the Optoma is much sharper and detailed, I think it's compared with the 9300.
Reason why I chose the 6700 rather than any quasi 4K and why LCD over DLP.
Firstly, the prime reason for changing projector is that I love 3D at the movies and wanted that experience at home. I'd been collecting 3D blu rays for years so I haven't been quick and it was now or never. Considering the in phrases are HDR, HLG, wide colour gamut, Dolby vision or whatever, etc, etc. 3D seems out of favour.
The middle son has just bought a 4K tv for his bedroom and I've wall mounted it. First impressions of the BBC beta iPlayer 4K HLG test image stream are what a fantastic picture. The detail, the colours, the sharpness and how bright the highlights were. Netflix and Amazon 4K were also very good. (Not as good as BBC)
Do I need that for my projector? No, l couldn't justify the sums involved to get close. I want a good/great picture with scale, (120") thank you very much. With 3D and great sound. If that's still 1080p at a sweet pricepoint. Even better.
Sorry, jaffa if I've digressed. I find the my epson 6700 to have a much better image than the hd20 (and I was very happy with it). Colours can't be compared, neither can brightness, contrast and sheer in your face wow factor. 3D yet to be tested, buying glasses. It really is a huge step up from my 2009 hd20.
Regards
Scott