wish you all the best with your new pc build...
and here is some ideas from me, and i hope they would become helpful to you.
try to import your stuff from abroad (atleast via an importer, there are few of them in sl now).... buying from unity plaza sellers is one worst and risky thing you can ever do!!! (from my very own experience)
going for 4870 or 4870X2 is worthy. and there are 4890s as well. they are cheap compared to nvidia cards, and give the same thing (almost the same!!) and If you are not planing to put two 4850x2 cards in future and if you are sure about that, there will be some advantages in getting two separate 4850s and putting them in crossfire configurations.
Take a look at the AMD phenom II as well.