Well.. I'd say it's impossible to do a 'true' comparison unless we're given a full control over the chipset/memory parameters. The bottom line is, motherboard manufacturers play tricks with straps/latencies for one reason (performance) or another (compatibility), and without that knowledge we really don't know what is going on underneath. (It was one of the main reasons I didn't, and to some extent still don't, like P965 chipset) As Yoxxy precisely pointed out, playing with subtimings can make one divider win over the other, or vice versa.
Said that, in current BIOS many motherboards employ, higher memory frequencies seem to give better performance than tighter timings. Especially when sub-timings are left auto, the benefit of higher frequencies are even more pronounced. (Except some stupid cases like 1300MHz/5-6-6 on 680i) In the end, we all know the timings/frequencies are relative to bandwidth, and different chipsets will handle things differently, not to mention different BIOS. The definite way to determine the impact on performance is testing your own, under the desired CPU/FSB frequencies. I find the 680i chipset somewhat more responsive to memory configuration than 975X/P965, but even then, the difference is so small that it really doesn't matter unless your family's living standard is dependent on your benchmark numbers.
P.S. Why do you need 2.40V for 800MHz/3-3-3? :shock;