I'll climb back up on an old soapbox here. I really believe in recording myself (I don't do it often enough, but I still really believe:). If you record yourself at slow tempo and then use software to speed up the recording you can see how you would sound at speed. It can be amazing how something that doesn't sound right at 60 BPM can really come to life at 180 or so. Also, if your timing is off at 60, you'll really know at 180.
Then, see if you can play along with your own recording at the higher speed, or find the fastest speed you can play along cleanly.
Handheld digital recorders have gotten pretty cheap and can transfer your recording to your PC im MP3 format, or if you have a built in mic you can just use that. Audacity or The Amazing Slower Downer are programs that can change the tempo of a song without changing the pitch, and they're free.