Have you tried 4.5 yet? MUCH easier to accomplish, and honestly, if 4.5 doesn't cut it, you may need to just live with it. A 5Ghz 24/7 OC on Ivy would be crazy IMO, without awesome cooling.
I took my 3570k up to 4.6ghz with hyper 212 and temp in mid 90s so I didn't leave it at that speed for long. I did do a few benches.
BF3 online 3570@ 3.4ghz average GPU usage of 670s was 50-60%
Bf3 online 3570@ 4.6 70-80% GPU usage.
I saw a guy with CPU up to 5.0ghz and 680 4-way GPU usage was mid 90%
My goal for my system is BF3 online 5760x1080 at120fps.