To be honest i haven't noticed anything, my 1000 takes a few secs to turn on and load everything up but that's mainly due to plugins. My slim is currently on 6.31 because i had some LBP stuff to dl from the store. Ive noticed in the later 6.xx updates they changed it so the LEDs don't blink when its online, so you can't tell when its communicating or dl'ing stuff.

Regarding the speed thing of 6.xx i suppose your right, when i turn it on and after the game boot the icons are there instantly. Not much of a big deal for me though, i don't mind about these things.