In the parser today there were two 8600 GS cards from MSI just sitting there. Taunting me. Forcing me to investigate so that I could decide where to put them in the database since I have never heard of the 8600 GS before. In the end I came to the conclusion that they are simply 8600 GTs with 400MHz DDR2 (instead of 700MHz GDDR3) and no SLI connector. The core speed and shader speed are the exact same as the 8600 GT.
What I find strange is the need for MSI to make up the 8600 GS name for these. They already have two 8600 GTs that have 400MHz DDR2 on them and guess what? They fricken called them 8600 GTs! Why the ruse MSI? Why are you trying to confuse us?