Sounds great with the money saved. And one other question. If I went with the Crossfire for furture CF, could I keep the 650tx and safely say that I could CF 2x5850 with the setup?
It might get tight if you have a few HDDs/other peripherals in there.
Also, I am pretty sure the 650 only has two PCIe plugs so you'll need to use molex to PCIe for the second if you ever get it.
Only a $10 difference though... Cut back on the HDD a little instead, honestly. Can very cheaply get another HDD later, but replacing a PSU is pricey.