8320 will provide 100% boost IF it were the bottleneck, but that's theoretical. You will see a substantial upgrade with an 8320 and I recommend it. And enable v-sync and play on ultra. These cards are meant to run at 100% for years, and stress doesn't affect it. It's the temperature of the card, to high and it will throttle and possibly and unsupported information states high temperatures degrade the GPU. HOWEVER nVidia can run at 95*C I think, or 104 or something. I forgot.
As for BF4, depends. I like BF-I had every single one...I hate BF4 as of right now. It can be a good game, but it is -excuse the language, FUCKED up. To the point where I plaay maybe 15min a day and get tired of it.
Just watch this and he will explain it, I only...