Aha, the Apple FBDIMMS are definitely closer to the MB, so that would explain it. Anyone have any idea whether that 76C is a problem? It's a good 8C hotter than the next hotter DIMM. Is it worth worrying about?
Not sure what to say about the one dimm, you might try swapping the dimms to see if it is the dimm or the position. i have 4x512 factory dimms in a1, a2, b1, and b2 and 2x1gig from owc (but they look like the factory ones) in a3, a4. temps are (a1, a2, b1, b2, a1, a2) 56, 57, 43, 43, 55, 54. i would assume that the 1 gigs may run a little hotter than the 512s, so that might explain why they aren't cooler than the inner ones, but who knows.
cheers.