So I have an A2 with an FN barrel and PSA BCG.

Never had problems in the past, but this past weekend I had a few FTE's.

Two were with brown bear laquer coated. Not exactly surprising, but I have never had that happen with that ammo in any of my carbines.
Bolt would cycle, but round would stay in the chamber, and it would try and feed a fresh round. I had to mortor the second round out cause it was stuck.

It also happened with some Golden Bear ammo, which really surprised me. Casings were not stuck at all.

So anyways, I installed the BCM extractor upgrade, which i know is meant for carbines, but I figured it shouldn't hurt this.

Question, should i go with just the heavier spring, or also the rubber o-ring?

I don't know the power of golden bear, but tula out of my twenty's barely cycles. I would bet your problem can be remedied with ammo more towards the hotter mil spec side of things.

I think you have the right ideas as far as upgrading your extractor.  But it seems like the FTE's you had were caused by non mil-spec--in this case lower-end commercial ammo

Obviously the ammo plays a part, but I have shots thousands of rounds of cheap Russian ammo with never a problem. Heck I've done some short one day carbine classes using the Russian stuff with no problem.

Funny thing about my problems was that the bolt had no problem cycling completely. Just didn't extract before trying to shove another round in.

I'd try the HD spring first, and then the O ring, second.    If the spring works fine, I wouldn't O ring it, IMHO !  

The O ring is usually overkill if the spring is new and can actually be worse than not using it... can hold on too tight. Is this a new build? It may just need a good clean and 100 rounds to settle in....