How can I tell my overclock limits?

I'm using the latest Omega drivers to overclock my EVGA e-GeForce 6600 Graphics Card. In case you don't know what it is, here is the link: http://www.circuitcity.com/ssm/EVGA...24390/catOid/-13011/rpem/ccd/productDetail.do

Right now I am at 325mhz and 545mhz on the ram. I have no artifacts or anything of the sort. Should I go up anymore? They say don't go past 10% overclock on stock cooling... Is there anything else I can do to make this crappy videocard better?

Have you tested with 3DMark 03 and 05, and PCMark 04 for stability? They way you tell is you OC a little, then you benchmark for awhile...maybe 5 or 6 times, then OC a little more and test again 5 or 6 times, and when you hit the wall, you will notice the scores will drop off. When that happens back up, and then go back up in small increments until you find the place where the card will not drop off anymore. That will be your ***benching OC***. Back off about 10MHz o9r maybe a little more for 24/7 gaming OC. Gaming will heat the card up more becasue you play over a longer period than the benchmark runs, so be sure to back off the max *benching* OC for 24/7 use.