Thanks to all for the insightful and helpful comments. This is a really helpful group of people.

As it turns out, I had a bit of a misunderstanding when I posted the question. I had generated the file myself, with Pianoteq, and since I was playing with the Pianoteq metronome going, I assumed it kept the metronome setting as the tempo in the midi file. But after posting the question, I played the file in Van Basco, and found that it assumed a tempo of 120. Then I dug into it and came to understand that some midi files do not have tempo info, and if there is no tempo setting, it is assumed that the tempo is 120.

So the solution to my problem was to use the Length of Midi Music feature, adjusting all notes by a factor equal to the ratio of the desired tempo to 120, then play in Power Tracks at the desired tempo as suggested by Mac above.

I learn something new every day.

Thanks again,

Ed