Does the performance of some Video cards/GPU on games scale linearly when overclocking high?
For example when you overclock HD7870 that has a stock clock of 1000mhz to 1100 mhz you gain an additional 4-6 fps on games but when you overclock it more to 1300mhz, will you gain another 5-8 fps or only about 2-3 fps?
^ True, but it is often more or less proportional in GPU-limited games/situations.
For example, I've got a 30% overclock on both core and memory, and that translates to ~25-28% gains in fps in the few situations I have that really tax my GPUs, which is more or less a linear boost.
It also depends on what card you have - some cards scale better than others with overclocking. For example, Tahiti cards (79x0) scale performance slightly better than GK104 cards (660ti/670/680) with overclocking.
It depends on what the performance limitation is of the game in question. If it's pure processing power, clock speed increases will have a noticeable effect, if maybe not a 100% linear one. If however the FPS is being limited by memory bandwidth or available VRAM, the overclock will have no effect.
Maybe core clock isn't you bottleneck then... Have you tried OC'ing the memory? Or maybe you are CPU limited?
Not cpu limited, my cpu usage never goes much over 50%. I recently got a 2560x1440 monitor and the single 7870 just isn't up to the task. I need to get another one. Sounds like you know more about this than me so quick question: I notice when I have the lowest fps in borderlands 2 my cpu usage and gpu usage are both well under 100%. Do you think it would be a driver issue or something else?