Tire size versus ET's street radials

I've got 6 leaf springs, but other than that stock. Like I say, I'll stick with 245's so what I want to find out is how quick can you go with a tire that small?
On American Muscle Car on TV they said a Mr Norms 440 Dart could get into the high 12's which seems quick for the skinny tires it had on it.
I want to stick with 14" wheels too, I've only seen 235 slicks for that size.