No harm in trying what you have before you plunk down any $$. If the 13 feels way off, you know a 16 may be more what you need. If it's close try a 14 or 15. I'm pretty sure when I first tried my CRT I bought a 15 and a 20! I thought I'd need the speed, settled down with a 10...Much of it also depends on where you are using it. Often, crazy speed on a track isn't as valuable as instant accel...try, experiment and above all, enjoy!

DM