The SX is lighter turns tighter and has more balls. I am a GG fan, but I have to bite my lip and say that the SX is a better bike. Mine is running V Force 3 reeds and FMF Faty pipe. 230 main with clip at the top. A great enduro bike.
They both have the same forks - Mazocs.
The carb on the SX is easer to set up than that Italian "thing" on the MC, but I think in 08 the MC went to a Jap carb.
Jarred has finished 2nd over all in Enduro and 2nd over all in Off road this year on the SX.
For me the KTM spares are easy to get. I can't comment on the cobra although I have heard that the GG and Cobra are simular.
The SX changed in 09 to a whole new bike. We have the 07, no problems. I think from 02 to 07 were much the same bike.
The MC is not a bad bike at all, Jarred just prefers the SX and so do I.
Hope that helps