I don't know for sure, but I doubt you'll notice a *huge* difference. According to newegg, XMS 2700 is supposed to run at 2-3-3-6, and value select only lists "2.5" as the cas latency. I would *assume* that means 2.5-3-3-6, but I don't know for sure. What are your memory timings like?
And no, your motherboard doesn't support dual channel DDR.
I wouldn't say it's worth the cost, unless you had a memory upgrade planned anyway. Or, unless your current timings are something like 2.5-4-4-7.