Bottom line, if you're in need of a sub-60mm tall low profile heatsink for a 2U sized PC chassis, the Evercool HPL-815 heatsink will do the job suitably at full fan speed. In fact, of all the sub-60mm low profile heatsinks Frostytech has tested the HPL-815 ranks 7°C cooler (at 4000RPM fan speed) than the next best thermal solution.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips