For Haswell i7-4770K, 4.3GHz is not bad at all without extreme cooling. You could go a bit higher but the temperatures in stress testing programs will cause throttling, as you have seen. But in normal usage, you won't reach those temps and throttling. You might consider that OC not stable or proven due to being unable to run the stress test for long, but that is your decision.

Forgot to mention a tip that may reduce your temps a bit. In the UEFI you'll find the CPU Cache Ratio (multiplier) setting, which is normally the same as the CPU ratio/multiplier. It has been found that the CPU Cache multiplier can be reduced relative to the CPU Ratio/multiplier, allowing higher OC's, apparently without a performance hit.

The Cache multiplier can be quite a bit lower than the CPU multiplier, and the PC will run fine. The Cache multi can be below 40 (36 - 38) while the CPU multi can be over 40. I am not aware of any rule about the CPU and Cache multi settings relative to each other, besides the Cache multi should not be higher than the CPU multi.