Here's a fusion classic, Red Clay, by Freddie Hubbard, as played by Lenny White. For a time this was one of the most-played tunes in the world among college-age jazz musicians:
Lenny plays really on the front of the beat here, in a way I think a lot of people would be uncomfortable with today. That's the way I tend to play, so I like having some hard data on what the best people before me did. I took a close look at it in Audacity, and calculated that the second measure of the vamp consistently averages out to being a couple of BPMs faster than the first measure. The tempo overall does pick up in a minor way; at Lenny's entrance, the tempos on the first two measures is 64 and 66. By the middle of the head we add about 3-4 BPMs, and the tune ends around 69/70. I took a look at the double time during the sax solo, and they do maintain the established tempo— there's no dramatic tempo shift with the feel change.