We found a surprisingly large performance difference between CPUs, including a 14% gap between the Core i7-3960X and Core i7-3770K, something we haven't seen before. It seems Borderlands 2 makes good use of the i7-3960X's massive 15MB L3 cache, whereas the i7-3770K "only" has 8MB.
The i5-2500K was only 6% slower than the i7-3770K, while the aging i7-920 was 13% slower than the i5-2500K and 18% slower than the i7-3770K. AMD's Phenom II X4 chips looked just as bad, especially the X6 1100T, which was 8% slower than the Core i7-920 at 49fps. The FX series fared even worse.
Initially, we couldn't get Borderlands 2 to run with the AMD's FX processors as the game would cause our test system to throw a BSOD on loading. Turns out, the Asrock motherboard we were using -- as well as most AMD 900-series motherboards for that matter -- need a BIOS update to correct this issue.
With the updated BIOS installed, the BSOD disappeared and we were able to test the FX chips. Sadly, the performance was way below our expectations, with the FX-8150 limited to just 46fps when paired with the GTX 680, making it 29% slower than the Core i7-3770K and 38% slower than the Core i7-3960X.
Regardless of their core count or frequency, all of the FX processors we tested delivered the same dismal sub-50fps performance. Meanwhile, we found the dual-core AMD Phenom II X2 and Athlon II X2 to be incapable of maxing Borderlands 2, which is optimized for quad-core processors.
Here we see where that 75fps limit was coming from. It seems Borderlands 2 likes highly overclocked processors, as the default Core i7-3770K limited us to just 65fps at 1920x1200 with the GTX 680, while we recorded a 26% performance increase after boosting the clock speed from 3.5GHz to 4.5GHz.
The FX-8150 didn't respond quite as well to being overclocked, delivering just 51fps at 1920x1200. Based on what we have seen from other games, we believe there is something wrong here and hope that a patch is released shortly to help improve the performance of the AMD FX series parts.