Lag is almost unnoticeable with GGPO… unless you’re playing 3s.
The reason 3s is so bad is that there’s no easy way to isolate the game state from the read-only state like sound files, graphics, etc. in Final Burn Alpha. It’s all just main memory, sprite memory, etc. So the bigger the game is, the bigger the rollback, and the more horsepower you need to avoid the glitches. I think the working set of 3S is around 9 MB per frame, which means if you’re running with 3 frames of rollback you’re talking about over 1 GB per second of memory bandwidth just to save all that state! If you don’t have a very fast computer, it’s not going to work well.
Given the source code to the game, you would only save the parts which matter (position of the characters, amount of life, etc), which would only amount to a few kilobytes per frame, which is like 1000 times less data you need to save and restore, and would be easily doable.
It’s alright, but it’s still not that almost-offline experience that you expect. There’s still enough lag for lag tactics to exist.
but hey street fighter alpha 2 is still a great game.