I'm just running a stock 750 TBird with ASUS A7V in an InWin S506 case (not overclocking). The heatsink and fan are the AMD ones that came 'boxed' with the CPU. Have a fan in the 300W sparkle PS and one in the back of the case above the CPU (none in the front).
Here's my temp readings:
Cover off, idle - CPU 114F, MB 91F
Cover on, idle - CPU 118F, MB 89F (!?)
Cover on, load - CPU 122F, MB 87F (again !?)
CPU temp goes up, MB temp goes down...dunno why. By loaded I mean I'm running a dvd movie, surfing the net....trying to get a bunch of things going at once.
Edit... readings taken using the ASUS PC Probe SW that came with the board.