Are you sure it's the SIS K7SOM+. These are listed as having ( the cpu on board ). These are duron cpu's.click here and I don't think you can change them. Even if you could, the maximum fsb is just 133Mhz.
The SIS K7SOM only goes to 133mhz, so the barton would not run at it's full speed. If it is this board. click here
So if it is either motherboard, the barton will not run at full speed as both boards have a max of 133mhz for the cpu.:-(