i am in the same situation as you, with roughly a 350-400 dollar budget
and i have read that the 4gb version of the 770 is not worth it at all even for the future as it can't utilize the vram...it's only use is for sli or dual monitor setups...i'm new to all this so i might not be 100% accurate though
the 2gb version of that 770 also has been seen to hit the same benchmarks as the 4gb version!
i am going to go the r9 280x toxic route (have one on backorder..MEH)...gl with whatever you decide.