Usually it is the center leg that gets solderd.
What I have found to make the bigest differance in my KT7A-R's is good cooling of the mosfets. I have a Panflow 120mm intake fan in the left side of my case. It blows over the video card, ram, chipset, and mosfets. If I remove the side cover (and the fan) the mosfets heat up a lot and the system will start locking up on me. The next step I am going to do is AS epoxy sinks on all the mosfets and see if this makes any further changes in the voltage readings. Thre voltage must fluctuate more then normal when they run so hot and this could be the real problem and this mod is just throwing more juice to correct a overheating problem. If this is the case adding 5v would be a backwards solution when what may really be needed is just better cooling. I don't know if when these boards were designed that they were counting on cpu's that consume so much juice and the parts in the power supply just get to hot from the heavy load.