Guys, first of all, please put your posts in the appropriate forum. It’s not rocket science and it would make our (two-man) moderator life a lot easier. This clearly isn’t a mix, music or show. Since it’s not about software or gear, nor an introduction or something to do with the workings of the forum itself and it IS DJ related (so not for the non-DJ forum), there is only one place left for it to go, DJ Booth!
On topic.
I agree with +/- 2 to 3 bpm (I use a percentage of 2,0 to 2,5) is about the max I’d go generally. Going faster seems slightly more forgiving than going slower. You CAN try playing with the key (if your software has that option) once you hit a speed level you think is better for the track, but which sounds hyper like Dievers said.
Another thing that has nothing to do with the “feel” of sped up or slowed down tracks, but everything with technology and sound, is that the more you change the pitch, the harder the software has to work. Especially on MP3s that means inducing so-called artefacts and this can become audible. Another reason to be moderate.
Having said that, you could bring a 120 track up to 123 or so and a new track in from 126, giving you a 6 beat jump in only 2 tracks (1 transition) which is pretty good.
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