GTX280 will be a better option by miles than the 275.
Also, a motherboard with dedicated SLI will be better than a hybrid board that does SLI or CROSSFIRE.
Needs bigger PSU, definately. 850W is not enough for two GPUs like that.
Why do you want 2 blu-ray burners? Why do you even want one blu-ray burner? Wait 18 months until they become $50 like a DVD brner is now... instead of $400 and $50 per blank 50gb disc.
Solid state drives are a waste of money unless you are running a server farm. Save your cash and get some normal drives with big capacity.
Other than that... it looks OK, though Ash already mentioned the thing about the sound card... don't use onboard sound unless it's good. My board came with an X-Fi card, which is partial onboard, and partial 1x PCI-E daughterboard.
A can't stress enough though how much better the GTX280 is than ALL other GTX cards, including the latest GTX295's. The 280 kills them all.
I'm not entirely sure what price difference you are looking at between the 275 and 280, but whatever it is, it's worth it.
*EDIT*
The HAF is a really nice case
I saw it at the Thermaltake show before it was released... I was very impressed by what I saw... have to let me know if it's as good as it "looked" at the time
~Sol