The rate that technology is going these days, 3.40 ghz will improve soon **gets out computer magazine.** Yes, I don't see anything higher than 3.40, but it's going to definitely rise, I'm pretty sure there. **gets out last month's magazine** Now I see 3.60 ghz there.
I run mine on a 300 mhz Pentium II processor, with 256 RAM I think. I wait a considerable amount of time loading scenarios or saves on big maps (I can't even say considerable, maybe a minute), but even then it's not bad. I have a friend with a fairly recent one, I forget the specifics, 3.0 ghz or something, and it's definitely much better than mine is, but it's not x10 better, so remember that 3 ghz won't be twice as fast as 1.5 ghz. My thought with computers is that whatever is expensive today will be cheap tomorrow (I don't mean that literally, but you get the point.)
However, you might want to upgrade the RAM. RAM is quite cheap and will improve the speed.