I started with a VGA cooler, then went to a Pentium class heatsink, then went back to the VGA cooler for overclocking (700), then the heatsink with a Pabst fan mounted on it for EVEN MORE overclocking (733), then for some reason I don't remember anymore I seem to have clocked it back down to 600, possibly because I was having trouble with crashes and wanted to rule heat out.
The thermal readout on the 750CXe does NOT give me sensible values (11-13 degrees C when overclocking in a room at 25 degrees? hardly), so no real data to report, unfortunately.
Voltage tweaking is not a problem.
I still say it's not likely we'll be using these boards very much in 2013, if the world goes 64 bit this year or the next (ppc970 sampling now, opteron shipping for months at workstation prices, sparc has 64 bit workstations and intel does 64 bit on servers), we'll start tagging along sooner or later. Remember that the 68000 in the A1000 is a 32 bit CPU, even though the external bus is only 16bit. From A1000 to A1 took so far 19 years, and we're still only at 32 bits. I for one will jump at the opportunity ;-)