I finally took the plunge and clocked up my machine, having originally purchased an i5-2500K with this in mind.

And here's a collection of 3D Mark benchmarks before & after...

Before OC:

4.0GHz @ 1280x1024:

4.5GHz @ 1280x1024:

4.5GHz @ 1080p:

With the 4.5GHz benchmarks, the video tests screwed up a bit, due to the SLI getting slightly confused by the new clock rating. Once I find a way to fix the SLI thing in 3D Mark, I'll post an update.