The command to show your FPS is "perfoverlay.drawfps 1".
The BETA is incredibly fun, except for a few annoying problems. It's only a BETA but, you know, can't avoid feeling annoyed by some stuff.
The XM25 Airburst is seriously overpowered. It can hit from incredibly ranges, it shoots fast and it has no damage falloff whatsoever. I'm not sure why there are even that many tanks allowed at once in the BETA. The medic's AK-12 is way too good. I don't know if it's the recoil compensator I have on it, which might be it, but it's almost a laser gun. Dunno why, but sniping seems incredibly easy in this game right now. Can't explain why that is.
Other than these and the unusual performance issues (with and without updated drivers made for BF4), this BETA has been incredibly fun and I'm enjoying it. Will probably buy it.