computer_nugget2 :
hmm you might need to remove the fan on the side panel of the case in order to fit that cooler, but other than that looks like you're good to go bro.
[edit] deus bro, hes from new zealand. you know that place next to australia. lol
OH! Sorry haha I didn't see the url. My bad.
As for the selection then, your 7750 and the GTX 550 are clearly weaker then the 7790 or the 650. If you go for the 650, I know it has better SLI support than the 550 so it's more future proof, so I'd say because it's weaker and less future proof you should eliminate it. The 7790 I think performs better than a stock 650, but AMD has issues with CrossFire in general, so I'm not quite sure when it'll be fixed even though they're working on drivers to fix crossfire stuttering as we speak. So I'd say the 7790 is the better buy overall since it's notably more powerful and they'll probably resolve CrossFire (if that's even a concern for you) soon enough.