Like I said earlier, the motherboard has no control over memory limitations as far as capacity unless they flat out tell the system BIOS to not register above X amount per channel. The memory controller is inside the CPU, provided the board has the maximum slots available, and the manufacture laid the traces properly, and didn't tell the system to Halt if going above 4GB occured, then you could infact use 8GB.
OCZ, Crucial, and G.Skill at one time did make 2GB DDR400 modules, but, if I remember right, that was in the $150 to $200 price range at the time per module. I remember paying around $100 for a 1GB module from OCZ back during that era.
So it's all going to come down to if I can find the CPU memory limitations, which is proving difficult since it wasn't really a specification people looked at as far as the CPU back then. I guess the key issue is, 2GB modules didn't exist at the start, and the manufacture couldn't test and legally say the boards could support more. It's just like the MSI 880g-e45 motherboard I have. The manufacture lists the MAXIMUM memory as 16GB, yet I have 32GB of DDR3-1600 sitting in the board running flawlessly.
Another thing people see is the consumer boards list they don't support ECC memory, but, if the extra traces had been laid between the CPU and memory, you could throw in ECC memory on some AMD systems, as a lot of consumer AMD processors back then supported ECC.
EDIT:
Didn't see your post trotter... If I am not mistaken, all of the dual core processors for 939 supported running ECC if you had a good motherboard.
754 wasn't that bad, I had a 60% OC on air with a newcastle 2800. Northbridge fried before the CPU ever went belly-up.