As for overclocking i would Google it and search for other people's overclocking experiences as per your card/model/manufacturer.. e.t.c
You can usually find a rough idea as to what you can expect, but as is the same with any overclocking - don't just crank it up and hope it works as you can damage your card, if not fry/break it.
So take it in small steps, and test each small overclock with all the standard benchmarks for overclocking - 3Dmark03/05
Personally i can't see any good reason except for having a benchmarking ego (ie: i have to beat someone else's score..) to bother overclocking this card yet let alone open up the extra pipelines and vertex shaders - their's no need even with high end games such as Doom3 or HL2 set at max..