If you want a notable difference in performance, I'd suggest a 770/R9 280x and up(if found). As far as not replacing the GPU, you can try OC'ing the proc from some added punch albeit minor.
overclock the CPU, that 6300 can match a stock 8320 at 4.6 Ghz in terms of performance. You can get more FPS that way too, plus lowering in game settings
If you want a notable difference in performance, I'd suggest a 770/R9 280x and up(if found). As far as not replacing the GPU, you can try OC'ing the proc from some added punch albeit minor.