I doubt the problem is in the motherboard or psu as he tried it in two more A2000s with the same results.
I would check with different versions of the software for the goldengate and also with new clean install of Workbench.
It may also be worth trying it on an Amiga 3000 or 4000, as it could have issues with the 2000 (unlikely but you never know). Perhaps the emulation needs a vga card to operate at full speed? Hopefully an experienced owner of this card will show up (try also asking at Amibay,.many people have them there)
Failing that I would look for some hardware bottleneck between the Amiga and the card. Try different slots, clean the card contacts with contact cleaner, and look for obvious hardware problems on the card (blown capacitors, does it take simms? Can you perhaps replace the memory? )
