In terms of games, the FX-8350 (4.0GHz) is already clocked 600MHz higher than an i5-4670k (3.4GHz). Will increasing the clockspeed to 4.5GHz make it equal to a i5-4670k (effectively just a vanilla i5-4670k) running at stock speed? That depends on the game. Going from 4.0GHz to 4.5GHz represents a 11.25% increase in clockspeed, however, that does not directly translate into a 11.25% increase in gaming performance across the board. It's not a 1:1 ratio with regards to an increase in actual performance, because all CPUs (both AMD and Intel) have inherent inefficiencies that overclocking simply cannot overcome. The easiest one to understand is the FX-8350. Just about everyone knows that every two CPU cores share a single FPU core. If both CPU cores are processing a thread that must have access to the FPU core, then one core will need to wait for the other to finish.
Some games don't really care how fast the CPU is as long as it is fast enough not to slow down the graphics card. One such game is Crysis 2 another more recent game is Tomb Raider. According to the following performance chart, Tomb Raider doesn't care if you have an i5-3470 (3.2GHz), i7-3770k (3.5GHz), FX-4170 (4.2GHz) or the FX-8350 (4.0GHz), they all have the same performance with a Radeon HD 7970. Boosting the FX-8350 to 4.5GHz would likely give you no performance increase whatsoever.
Unlike Crysis 2 which didn't really care too much about the CPU, Crysis 3 does care. Below is the performance chart for that game with a GTX 680. The i7-3770k get 64 FPS while, the FX-8350 get 60 FPS; a 5% difference. Since it can be easily seen from the chart that the CPU does matter, I would say that a 11.25% increase in clockspeed should mean that the FX-8350 @ 4.5GHz should match an Ivy Bridge i7-3770k at a stock speed of 3.4GHz (and likely the i5-3670k if it was part of the benchmarks).
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