Most of the people posting that these "low spec" setups are "ok" are probably still in Azeroth. Outlands is far more graphically intensive. I wouldn't say anything less than 30 FPS on your alts is acceptable for PvP and 60 FPS (Monitor refresh rate) on a main, anything less and you're handicapping yourself by lowering your reaction time.

Additionally, on a lower spec machine, you will inevtiably lose follow a lot more often due to the follow algorithm not executing often enough.