The extra 100 lumens does not equate to much because those are manufacturer specs not real specs. Both the 8700 and the MT800 will work best in dark/semi dark rooms. Chances are you will not be using it in a sun filled room. The 8700 does have a higher contrast ratio...to me that very important. But is it really 140 ansi lumens less bright than the MT-800 once calibrated. The MT-800 has the bigger DLP chip with 7 color segments but has a brightness uniformity issue which drops to 40% on some corners. It does have a great Faroudja Chip for De-interlacing/scaling. Your best bet is to jump into avsforum and ask the experts...which of course you already have done.
The price difference on the MT-800 does not justify its features. I would go with the 8700 save your cash and get a new one in 3-4 years(if even that long)...which based on your level of gear will mostlikely be doing. Did you look into the higher end Optoma H77? The Optoma does really well with colors/contrast for some reason.
Stay away from Draper..I personally think they have no extra outstanding features. The screen is equally important as you know. Go with a Dalite or Silverstar as some have mentioned. If you want bright in ambient light go with any Dalite with the Hi Power fabric.
I am totally amazed with the contrast ratio and color on my Optoma H30 via HTPC. The 8700 and MT-800 is even a tad better supposedly since I have not demoed any of the two.
happy huntin.
