I would do the video card as first priority and then RAM. No real reason you need anymore than 12-16GB of RAM though, unless you are running some memory intensive stuff while you game
For reference, my Q6600 with a Raedon 7870 and 8GB of RAM runs Bioshock Infinite very well, so I doubt you would get much gain from upgrading or overclocking your current processor. To clarify, my processor is way worse than yours and RAM is essentially equal.
The 7870 benchmark is about 4200 compared to 1049 for the GTX 295, so that's the big difference.