DANGER Will Robinson
You don't want to replace the stock cooler on a GF FX 5800 Ultra with anything that fails to cool the DRAMs. The DDRII memories on the 5800 Ultra need cooling as much as the GPU.
Notably, the Zalman and Thermaltake heatpipes DO NOT cover the DRAMs on the graphics card, and therefore are NOT appropriate for DDRII memories on the following consumer cards: 5800/5800 Ultra/Radeon 9800 Pro 256MB only (128M uses DDRI).
I used to drive a Heisenberg, but whenever I'd glance at the speedometer, I'd get lost.