You will not see a huge performance gain unless you are overclocking your memory, then you may see a 10 to 80 MHz increase in ability to OC higher then you were able to before the heatsink. Good heat sinks for memory is almost as expensive as getting some fast DDR2 with them installed already (OCZ Reaper has some massive cooling). DDR3 has heatsinks installed since most runs native at 1.9 volts or higher. Most good memory anymore has some sort of thermal dissipation built on. It is actually attached with thermal tape stuck to the modules. It can be removed with a razor and a little pressure to separate it from the module itself.
I would not invest in this, waste of monies in comparison to the gains IMHO.
TD
