Absolutely. That's what I did first when I started with my KT3Ultra and my XP2100+. So long as you can maintain the more agressive memory timings, up'ing the fsb synchronously results in better performance, even with a clock speed that is relatively close. Of course, I've also overclocked mine now (1846Mhz from 1729MHz), using a fsb of 161MHz asynchronous (the best tradeoff between agressive memory timings and fsb speed, for my rig.) This took much benchmarking (of video performance, memory performance, processor performance, etc.) to cover all the areas, and repeating for each fsb/memory timing combination I tried, until I was satisfied that I had a decent compromise. I also found that while some of the benchmarks were higher with certain settings, others actually decreased, and system stability wasn't completely tied into the maximum processor MHz NOR the highest fsb. There's some sort of complex interaction between the different possible variables that made it stable at 180MHz fsb synchronous (one successfully tested example) while in another it wasn't with only a 167MHz synchronous.
I spent a few weeks playing with this, as several friends can attest. Ask |wm|crashdump or |wm|pneumatic about all the times they wanted me to come play UT and I just replied that I couldn't: tweaking.