I used to do this a lot. What I discovered is that it really depends on your mages. If you have 7-8 research point mages, then you can probably afford to take the -1 research hit and go drain 2 with the intent of spamming forts + mages to catch up with other people who have +1 magic.
If you don't, and a good example would be a nation like EA Abysia, or MA Man, you're locked into having at least magic 1. If you take drain 2, for instance, with EA abysia, your prime researcher only produces 3 points of research per turn. I shouldn't have to explain how abysmal that is.
What's really happening is that the lower research your guys are, the more an improvement percentage wise an increase in the magic scales are. The higher researcher your mages are, the less relative benefit you're getting out of it.
Jazzepi
Jazzepi