I'm building a Socket 939 Athlon 64 setup (the fastest 800 MHz FSB on 939, an Athlon XP 3400+ Venice core) and I'm working on getting a graphics card for it. I'm thinking either 6600 GT, 6800 XT, or potentially 6800 GS/GT but that may be a bit fast for the CPU, I'm not as familiar with this era of hardware as I am late 90's.

Anyways, some XT's have heatsinks that cover all the memory, while some have a heatsink that only covers the graphics core itself. I know clock speeds/voltages can be different between graphics card vendors using the same chipset, but if the heatsink visibly covers up both the memory and the GPU itself (I can't see if it's actually touching the memory or anything from the angles in pictures), it it safe to assume I'll need thermal pads for the memory when I change out the thermal paste? And if so, what thickness would most likely be the best bet to get (1mm or 2mm, etc.)?