Seriously?
Any idea why?
3.9 is pretty much 3.5 with bug fixes and some _optional_ crap offered along with it. I seriously don't grasp all the "oh my, 3.9 is so slow" mantra that some people seem stuck with. The only thing that can slow down 3.9 compared to 3.5 is picture.datatype, which is a "fat" (powerpc and m68k) binary in 3.9, but which is also easily replaceable. Anyone with a pimped up 3.1/3.5 install would also replace picture.datatype anyhow.
