Just wanted to let you guys know that the problems with the ACA620 have been solved. I've found a metastability bug in Gayle, which made the computer hang every now and then. While I was at it, I also fixed the problem with the A300 boards (A600 boards with old -01 Gayle chip and GAL-fix). The metastability bug in Gayle is more easily triggered when the chip is hot, so the problems appeared like thermal problems on the accelerator.
Those of you who already have an ACA620, please contact your reseller for an exchange/update.