my guess is yer still running at 12.5x. you could run CPUID to see for sure (or watch your boot screen before it changes).
but i really think this board will default back to 12.5x for anything you put in higher than 12.5x. as far as i know, it will NOT run that chip at 13x without doing something like the wire mod, since that chip's default multi is less than 12.5x. if it were a XP2600+, i think it would not go BELOW 12.5x (since it's default multi is above 12.5x). don't have one of those, so i can't say for sure.
take a look
here. in the drop-down menu across the top, choose Socket View, Barton, skip the Vcore (adjust it yourself in bios), choose 13xfsb.
what you'll see pop up on the picture are 5 little black lines, each connecting 2 sockets on the mobo pcb together. these black lines represent the copper wiring you'll use to do it. this will force the mobo to a 13x multi. simply choose "AUTO" in the epox bios and it will go to 13. you could also force it to 13.5 and others higher as well. play with the multi drop-down menu and you will see the wire arrangement for that combination.
it's very simple. use a single strand of speaker wire, cut into 5 very short pieces that you can bend into a "U" shape. using a steady hand, put the ends of that "U" into the 2 corresponding sockets. repeat with the other 4 pieces. slap the chip in there. close it all up. reboot into bios (making sure it has AUTO for multi and the FSB you want to use). check for stability.
i got my 1700+ up to a 15x multi @166fsb into windows, but 3dmark failed. 14x multi worked fine for 3d apps, but prime95 failed after a few. so i settled with 13.5x. everything stable.