boom,
Your speed will definitely increase, however it will not guarantee your revs to increase. They might, but not for sure. I know when I switched to 15lbs. around 8 years ago, I gained about 1 1/2 mph in speed, but there was no noticable difference in revs. I have seen the same for several other people.
--------------------
Who needs a 300 or 800, when I have a 294 and a 295!?!?!