The [A] version can run 133mhz fsb with max 140+. Your current is a 100mhz fsb with max 115 +/- 5. The performance difference is ca 5%. If getting a new board the [A] version is the way to go. Upgrading from KT7 to KT7A is however hard to justify unless you can sell the old one for good price.
Eriksson is right, I just bought a KT7A at the turn of the century, popped a 750MHZ processor and overclocked sucessfully (so far) to 933..(Still breaking it in).
This board is incrediably easy to overclock, all you have to do is get the latest "overclockers" BIOS flash, hop in the BIOS, change your FSB (this BIOS refers to it as Clock by slight adjust) to your desired (MAX availabe is 135) and set your multipliers to whatever... (MAX available is 12.5) and it hums like a dream.
I haven't had an issue overclocking the KT7A, not to say that the KT7 isn't a good board, the A board is probably your best bet if you plan to overclock on the high side.