One thing to consider with a higher end GPU in a stock system is its power consumption. The PSU may also have to be reconsidered as well.
Yes good point.
Using a PSU calculator found here that system including the video card I mentioned uses up to 425W.
On the link provided where you want to build this system the Antec & Corsair 550W or 650W are the ones I'd personally get but the XFX 450W is a recommended PSU in that calculator. You're better off with a bit of headroom though if you upgrade parts later on.
Don't know how much that will break the bank as the case in your initial list had a PSU with it.