Quick question; is there some sort of conversion from the rate of fixtures per minute to beats per minute or a way to change from FPM to BPM when assigning effects to a group of fixtures?

In the smartFX editor there is a drop down next to the rate field. If you set it to "per fixture" then the rate value will be applied per each fixture. If you set it to "per cycle" the rate will be applied for the entire group of fixtures selected.

Example. Int. effect over 8 fixtures at a rate of 120.

Per cycle: The whole group will flash at a rate of 120 bpm. This will be a very fast effect.
Per Fixture: Every fixture in the effect will flash on/off at a rate of 120bpm. This will appear as if the lights are chasing in time at 120bpm.

The rate value is always a bpm value. Just play with the per cycle/per fixture parameter and see if that's what you're after.

You can also just divide the desired bpm by the number of fixtures and set that in the rate field with the "per cycle" parameter selected.

Hope this helps!
-Tyler