I've been playing sessions for over ten years now and a question like this is not really necessary if you think about it. But I'll try anyway. The speed that you play tunes can be different from one time to the next. So much depends on the situation or the mood of the players at the time. Or, who started the tune. If someone is intentionally taking an easy pace on a tune and the next time someone plays it they start it with more energy, or in a medly with other tunes it will sound different. And I say, "Viva la differance!" However, in the case of certain typs of tunes you must make a distinction. For example: I hate playing slides like jigs. They sound dumb that slow. They're written to be played kind of like slow hornpipes (wich makes them sound like very fast jigs) but to keep them from sounding like really fast jigs you think of them as slow hornpipes. Speaking of hornpipes, try playing them like reels and you'll find out why they're hornpipes. The whole point I'm making here is to let the music itself dictate the speed. Also use common courtesy with your fellow musicians so that everyone enjoys themselves. If people at the session can't play up to speed and others can, play a few tunes slower, (ones that those players suggest,) and when they're done, cut loose with tunes the way you like them. If you're making time for the novices, they'll be more inclined to let you have at a few tunes too. And they just might sit them out to keep from bogging it down. Well, I hope this might help... good luck.