RivaTuner can be gotten <A HREF="http://www.guru3d.com" target="_new">here.</A> It is a pretty comprehensive o/cing tool. As for the overclocking itself, basically the rule of thumb is to overclock in 5-10MHz increments and when benchmarks start to show artifacts such as "snow", lower it by 10MHz. That way you won't have artifacts and it should keep your card within safe temps.
I have a gf2mx, but the tweak program i use will work with any nvida card. It is the gtu (Geforce Twek Utillity), from gur3d, and very good it is. I have used it for over a year and sware by it. I can get 10% speed boosts with no oc. Your oc percentage is right for an asus card the oc very well. Ram is the main thing to oc these days. If you are stable with a 10% increase on either not both, oc the ram. Go to <A HREF="http:// http://www.gefrorcetweak.com " target="_new">http:// http://www.gefrorcetweak.com </A>.
Open your display properties window and you can check it there. Also you can overclock with Rivatuner and then check the box for apply these settings on startup in the display properties box. now when windows starts you will automatically get the overclocked settings.
For example my TI200 only shows 220/500 in the display properties box. But at startup my video card gets set to 232/464 by this little trick.