FPS is anywhere from 40-70 average.
Latency is a steady 20-40ms on home an world sides. If it spikes up it's usually someone using uTorrent on another PC in the house and drops back as soon as it's closed.
Back before I moved I had roughly 250-300 latency consistently and it was very frustrating to judge distances between players. I would bladestorm on my war in WOTLK literally on top of someone and not hit them but when I kited other wars BSing I could be 15 yards away and still get hit. Dont even get me started on jumping charges.
Now Im rocking 20-30 and DEAR GOD its so much better, especially as melee. Acceptable is kinda subjective because I got my highest rating during WOTLK with that crap latency but I would say for the sake of sanity stay under 150.
Depends on if you play caster or melee. Playing a melee with 100+ latency really sucks. Constant range issues even though you are on your target. Can't kick when you instinctively want to kick, have to take latency into account.
As range it's not so bad. Interrupting is still different but casters forgot how to interrupt and just blanket nowadays. What sucks about latency on ranged is LoS issues. Ever get sheeped while you are clearly behind a pillar los of the Mage? I think it's because the Mage has crappy ping and on his side you are still in LoS even though on your side you aren't.
I cap my fps at 60 on ultra because huge jumps or drops in fps causes distracting shutters on screen. My latency is 60-80.