Overclocking increases performance, yes. It also increases the amount of heat generated by the card, and the amount of cooling needed (small amounts of o/c may be covered by the existing fan/heatsink).
But it also decreases the stability of the card. Overclocking can cause games to crash, artifacts to appear in game, model distortion, problems with texture loading... the list goes on.
The best solution when your 4 year old graphics card (in the computer world that's like being 40 years old..) can't handle the games anymore is simply to replace it. A GeForce GTX 260 only costs around $160. That's about 9 mowed yards (at $20 each, with an extra yard for Shipping/Handling).
* Updated game trainers and cheats daily
* Get notified when new cheats are added
* Request which games get new trainers
* Priority support with any problem