The highest gear doesn't matter, the smaller the chainring, the lower the gear, and therefore the more the torque on the freewheel threads. When I said 25, I was referring to your largest rear sprocket, which will give the lowest gear available when combined with your small chainring. That was the number I was giving.

I'd also suspect ThermionicScott is right, the freewheel threads are probably just full of the remains of the hub threads