The 133A boards will only run with the FSB and RAM in sync. But the older 133 boards cannot get up to much higher FSB's. However raising the FSB should not give that much of a performance boost because it is double pumped making it effectivly faster and with a greater capacity then the RAM bus.
So a 133A based motherboard is will not give much of a performance boost except when doing disk intensive applications like Video Editing. But only a 133A (or AMD760) will get the FSB up to 133MHz.
I hope that helped but I cannot really see a reason for the upgrade. The new boards are at a price premium and don't give a huge performance boost