I own a Leadtek Ti4200 128Mb card, there's a thread about it's overclocking in this forum....
I overclocked the card to 300Mhz GPU, 540Mhz RAM, and i think the RAM can go up even further.
I recommend Leadtek to you, because their cooling is great for overclocking, but it is wise to have a well cooled case too
<A HREF="http://www.geocities.com/mol_gen" target="_new"><font color=red>My Computer</font color=red></A>