At the moment a lot of memory manufacturers are carefully probing if there is a market for 4 GB kits in DDR2 Non-ECC variety. However, Mushkin is the only one who offers a hardcore overclocking kit that runs DDR2-1066 @ CL5. Many other companies have that at CL6 or even worse. Of course this means that the price of Mushkin's XP2-8500 4 GB memory kit is higher, because each single module has to be tested individually if it can handle the high clock speeds. With current 128M chips the number of modules passing these tests is very small, which explains the price premium.
These modules are certainly not for the average computer user who runs everything at stock clocks and mainly uses Internet Browsing, E-Mail and Word Processing. On the other hand gamers and power users who are constantly using demanding applications and games may find this memory kit a viable choice. Another possible use of this memory I see is when building a server that needs a lot of memory. Using current Intel platforms you can build a cheap Quad-Core system with 8 GB of memory without going the expensive FB-DIMM route.
Despite the high price I decided to give this amazing memory kit our Editor's Choice Award, because it is simply the best (and only DDR2-1066) 4 GB kit on the market at this time.