There is certain benefits. Somewhere out there there is an article on that. The idea is, that you'll get up to 20% improvement of the performanceif you OC both GPU and memory. OC GPU alone doesn't give you almost any improvement.
Speaking of my experience going from defaults to 190/185, I've got a score of 4260 (from 4104). Haven't pushed any further, as I know, that at 200/205 (many get that far) my system failed to complete the test and I see too much of the junk on the screen.
Another point is that I'm not sure how OC influence the TV-out. My guess is - no good, as I suspect that was the cause of my initial crash.