4770 or 5750 worth it or useful.

I have a 390W Cooler Master Plus PSU and a Low end Rig. I'd like a Cheap card that will last me some time.I play at 1440x1400 only, not higher.

I seem to have 2 Options-

1)Buy a 9600gt or 4670

2)Buy a 5750(dx11 games) or 4770. But are they much better or Useful to me. Will they Work for the psu?

Links of PSU are-

http://www.coolermaster.com/product.php?product_id=3746 ( I will have to use adapter for 6 pin)

PSU Calculator calculations:

http://web.aanet.com.au/SnooP/psucalc.php (Recommends 250w???)

http://extreme.outervision.com/PSUEngine (Recommends 290w)

Why the Discrepancy?

5750 and yes itll work.Human-after-all