I just bought one for a mates S939 rig off ebay, if you end up going that route avoid the top 2 models of either the X2s or the Opterons (180 & 185) as they go for stupid money, I bought an Opteron 175 at a relatively bargain price of £60

. Naturally to make up for the lower clock speed you can just overclock it a little

.........which reminds me I need to get my mates 939 rig a new HSF for that.