Yeah, CPU speed could be a factor. Mine's 3.4 GHz, and I get no such lag with Dust or anyone.
CPU speed and type is important. If it's a Singlecore, it's no wonder you're not getting fullspeed, as I have a friend who has a low-end Intel dualcore and she has no problem getting a full 60.
Sound lag, reduce the latency, yes. Obviously the lower the latency the closer the timing, but if you're going too fast for your sound/audio system, it can begin to skip, pop, and warp. Remember it goes by milliseconds, so a value of 100 means that there will be a .1 second delay between when the sound should play and when you'll hear it.
However, sound lag can also be introduced a bit because you're not getting a full 60 FPS.
NarugaDenka: Is there some reason you don't want to upgrade? r1888 is VERY old; there's a lot of bugs that have been fixed since then and a lot of features that have been added. (Although some things do not fully work yet under the new GUI.)