There have been massive increases in performance with projectors since the 5700 was introduced in 2003 so as you already said any current 1080p machine could be chosen to replace it.
You need to decide on a few things to determine what is best, the budget is first, followed by what are your room conditions (batcave/normal living room etc) size of screen required what viewing distance what is your video source and what type of screen do you have (white/grey and what gain).
I see you already have an 8ft grey screen which will be ok for 2D material but if you want a 3D machine (they are pretty much all are now anyway) and want to view 3D movies unless it has some gain it may not be bright enough depending on your room conditions.
Once this info is known you can get down to selecting 2-3 possible projectors to demo and select from those which best suits your needs and preference.
Thanks for reply even now im quite happy with the picture but just had a quick google and i see the infocus 8600 for £650 considering i paid £2100 back then for the 5700 do you think thats all i need to spend to surpass it. I watch films in darkness 14 feet from screen and have yet to go to bluray i know but with 700 dvds will upscale until 4k2k comes in bit also fed by virgin hd box as well so is it worth my while.
well watching from 14ft depending on the screen size you may not see that much difference going to 1080p. The 8600 would be a cheap way getting into 1080p until 4k comes along but I would consider moving your viewing position closer to around 10ft especially if you start buying into bluray.