well it sounds to me that this build is going to be a bit of a temp build until *decent* quads come down in price. Baring in mind S775 is about to be removed from production, i would make sure you get the case you want then just build up a budget PC around that. For this reason you are probably better with the E5200.
I would tend to disagree with goin as cheap as CAT is suggesting for the motherboard because it will be extremely limited all round and it sounds like you want to do a bit of fiddling which would result in some serious frustration. I would maybe even recommend spending a couple quid more than the one i suggested and getting something from Asus or Biostar.
This is a build with a much nicer case
The RC 690 is very popular and a lot of people have had a lot of success using it