I had no idea about this pixel shifting and other methods, but you was was right, most the projectors under £5k seems to be some sort of 4k, but not real 4k, all a bit of a fix...........
So I called Richer Sounds who have always been great, I got the projector from them because of the 6 year warranty they give, I have had it 4 months and they have agreed to take in back in exchange for the Sony which is getting all the rave reviews at the minute, so great service.
I was happy with Optoma, it really does look stunning, but its DLP and I can see a rainbow of light every minute which I am told some people see it and some dont, so thats the main reason for the upgrade, but I did feel a bit cheated thinking I had a 4k setup.
I know its not the cheapest place to get it, but with the 6 year warranty and a free Sony UBPX1000 4k bluray player which is not a cheap player makes it a good deal, have to wait 2 weeks now until they get stock from Sony.