i5-750+5670 would give you the better performance, and would be more future-proof although not really. It'd be better to get the i5-750 because, you could just upgrade your GPU along the road, and it is much easier to install than a processor.(incase you want to upgrade.)
I feel the I3 setup would be more powerful now as the 5770 is around twice as powerful as the 5670 but as virrze mentioned if you think you might want to simply upgrade later the gpu is alot easier to replace than a CPU
The 5770 rig will be a excellent gaming machine, right out of the box. I wouldn't pay for a rig with a 90 dollar 5670, with intentions of changing it out. The dual core, hyperthreading will be a good gaming cpu. Its a compromise from a quad, but thats what budgets dictate
The HD5670 really isn't appropriate for your resolution so the HD5770 is the way to go. The i5-750 is certainly the better processor but the I3-530 is alright at stock and could even be quite good if you overclock it.
Are you talking about prebuilt systems or are you building your own? If you are building your own system and you are on a tight budget then a Phenom II x4 system is the way to go to get the most gaming performance for the money. Just yesterday afternoon in another thread I found some nice combos/deals for someone considering the same. Let me see if I can find it.