OK, I apologize for being the ignorant dumb f*ck.
It would seem that when I upgraded from TMI to NEI (hey, it gets useful sometimes ), my SSP map somehow cleared itself of some BC addon pipes. I didn't use many of them, but the lack of the ones I used caused some of the Forestry fermenters to run dry of water, consequently stopping the production of biomass which crapped up some machines causing the pipes to spill items on the floor. Sh*t, some chain reaction. Anyway, as this was only a very small and insignificant part of the whole system, it didn't cause lag big enough to notice instantly, but it caused the framedrop I described.
So yeah, I fixed that, adding some recycler overflow protection for good measure, so that it shouldn't happen again (and goddamit, I have to finally upgrade from pipes to tubes ). Then I stopped the cobblegen, which almost instantly (once the tubes cleared themselves of the debris) increased the framerate to the value it was before this whole mishap. Conclusion--wind towers are lag-free. Woohoo!
And maybe I shouldn't brag about it, but in order to decrease the lag caused by many blockbreakers in my cobblegen, I used immibis' TubeStuff Duplicator to generate the same amount of cobble the cobblegen was producing. Heck, it may be called cheating, but it doesn't require 40 block breakers to operate and instead of ~40 cobbles traveling down the tubes constantly, I get a neat stack of 40 every few seconds. And besides, let's face it. Cobblestone generator doesn't require any additional resources anyway, so the purpose of this solution is purely to eliminate lag, not to cheat... much.
Yeah, I'm just excusing myself, aren't I?
Anyways, thanks for all your invaluable hints and explanations along the way. They, and your whole guide, helped me greatly.