dude this is a very tight situation we live in.... deikhu, let me describe this simply as possible... Technology is ever changing and we live in a competitive world... As u talked about Sandy Bridge and New AMD GPUs, yes they will be better but the thing is a new thing will be just around the corner, if u believe ur 100k spending might go to waste if u spend moeny now, is plausible... i would say go for it, no one lives for ever, haan but keep in mind the things u will be getting should have some sort of future proofing... If u ask me, the New Sandy Bridge will better because it will offer integrated Graphics aswell which wont matter much once u will be spending on a good GPU.... Regarding new AMD GPUs, the new line up which will be slighlty better than the older one.... Its better if u stick with Nvidia this time around...
If you want a Build Quote from me, just holla back.... happy to help