well you should just go for the gts 250 for the following reasons-
1.At your resolution the GTS 250 performs exceptionally well and actually with your proccy(CPU will become the bottleneck) you can get no GPU which can max out crysis with consistent 35 fps.With your proccy the GTS 250 will be able to max out many other games such as prototype....etc.A GTS 250 can do better with a quad core as you can see here
http://www.tomshardware.com/reviews/geforce-gts-250,2172-5.html,so the thing to note is that a dual core is also type of a bottleneck in games utilizing the prowess of a quad core.
2.Directx11 does not really matter in your case,not only because there are very less game utilizing it but also because the level of performance of the GPU's you are looking at like the GTS 250 and HD 5770,they would not be able to max out a game utilizing DX11 at it's fullest.So it does not really matter.
3.It's great VFM as it is selling for around 5k in various retail stores(even lower) like cost2cost and SMC(they maybe haven't updated their site about the GTS 250's price because they still show it as around 7k but you can contact them on TE itself and i am pretty sure you would get to know the real price),Whereas a HD 5770 will cost you around 7k(around 6.5k-6.9k to be exact as on cost2cost).A 450 GTS is also costing around 7k now.Now it's really upto you but i don't think a HD 5770 would be necessary and a GTS 250 should easily suffice for your needs as it does mine.Cheers.
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The PSU you mentioned is available for strict 3k on the site you mentioned so IDK how you got that wrong.And as everyone says there's the FSP Saga II for rs.2330.