Hmmm, in my case I got up to the last Phanon gen with no particular issues, as my performance did degrade slowly throughout the days, I didn't experience a fairly sudden drop like you (and I was able to turn the plugin off, although it didn't really make a difference).
The first generations should be thoroughly playtested (being the first that everyone plays), even though not as much in this XRM compliant version (but Teleth hasn't really revolutionized the code, so it should make little difference), so I'd wager the Phanon pileup is a symptom more than the original cause.
As for the bounty tasks, Paul mentioned they should be fairly simple and lightweight, as they only manage the bounties data. The really heavy plugin would be the core one that handles weapon dealers, research stations and various other fancy things. I suppose if you turn off the bounty feature from the AL plugin menu they won't be able to come back.
And while SETA does indeed make things worse in such instances (it's strongly recommended to not go past 6x in XRM, btw), there's no way a 5.2 GHz CPU should get
this affected if things were working as intended. Me, with an old and cheap 2,9GHz AMD I'm asking for trouble when setaing too much, especially in XRM, but him?
I also did play XRM+Phanon to the death several times back in TC, with an even worse rig and still using seta fairly extensively (10x, even), never had such an issue. Though there was no fancy bounty system at the time, iirc...