effective rpm range

The cam itself is more likely rated at 2 - 6G rpm's. The intake style will add a few RPM to the ceiling. Considering the small carbs on top, which is the biggest reason you feel a reasonable low RPM range at all, it'll still more the low point of the power band up some.

I'm with wild and crazy guy on the band. That's my guess and seems to make sense. I could be wrong.