Graphics card RAM Cooling

Folks, I have upgraded the combined heatsinks and diddy lil fan on my Nvidia 5900 XT card with a single water cooled block (along with the processor etc.)

Problem is - having taken off the combined RAM sinks, i'm getting the odd freeze up which i reckon is probably the card - RAM getting too hot?

It's running over stock (as it was before the water upgrade) at about 435mhz core and the RAM at 700mhz and it was fine before that.

FSB is o/c'd to 209 mhz (slightly up by 9mhz from before the water upgrade) on an Nforce 2 board with the AGP Bus locked at 66mhz.

Any views on adding heatsinks (or otherwise) appreciated.