Dave wrote:
Reason I'm asking is that the B&W 5K I happen to have specifies "SWR
less than 3:1". I know over almost any and every one of the five bands
my new beam covers (10, 12, 15, 17 & 20M), it'll be higher than that
at many points.

i would expect a pro 57b to be well less than 3:1 across those bands..

I would expect the 3:1 SWR limit is at the rated power.
Reduce the power level and the balun will survive an
SWR higher than 3:1. If it is rated 3:1 at 5 kW, hams
shouldn't have a problem with a slightly higher SWR.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com