As for min speed, max bank - no:
At Vs, I cannot roll out of wings level/1g or I'll stall - I'm confined to a straight line, so it's not that.
You have to find the minimum speed at which you can sustain the max angle of bank for the duration you need (e.g., 180 degrees for your mountain scenario).
For example (and these are artificial numbers, so you'll have to research your own for your airplane), the minimum level speed in a C172 -- without going behind the power curve -- may be available at 20 deg flaps. At full power, you may be able to maintain 60 deg angle of bank (2 Gs) for 180 degrees at 60 knots. Your min radius will be attained in that configuration.
Since such performance numbers may not be readily available for most GA airplanes, you'll have to interpolate and analyze available data, then test in flight at a safe altitude.