Tulu - seems like that cpu is going to be stubborn. You could try lowering vFSB back to 1.42 - 1.44v, and raise GTL's one 0.05x step at a time up to perhaps 0.75x.

I think you may need to just give it more vcore to get it stable at 3.4GHz, some 6600's just won't do it easily, pity about your hot climate though. Perhaps try 3.33GHz at the same vcore you are at now? I don't think you will get solid stability out of the GTL or vFSB adjustment, but you could possibly raise the max bootable/benchable FSB by a few MHz.

@jas420221 - I suggested that because it's the quick and easy method to see if higher GTL and vFSB will assist the overclock - as you know, GTL is derived from vFSB, and both GTL & FSB has shown to help certain people OC quads, especially the 65nm's - trying each at a time of course is more accurate, but I wanted to get somewhere fast, rather than take days to establish whether it was going to help or not.