"Correct tempo" is a curious thing and a bit of a movable feast, depending on which country you're in, which tune(s) you're calling "polka(s)", what dances you're doing to the tunes and what the specifically local traditions might happen to be at the time you're playing. And then there's the ability of the dancers and the caller. I'm sure Cap'n Birdseye is on the money for Cork and Kerry but they're not the only places where polkas are played and danced to. On an international forum like Mudcat you'll get "proper" (as well as "good") advice from all corners of the globe.

Like Bob says, "Watch the dancers!" And then play to them.

Cheers, Rowan