I've flown two models (and several airplanes) that might shed light on this discussion. I've flown several supercubs with the O-360 180 HP conversion and the only differences in the O-320 150 and/or 160 HP conversion are better short field take off, better climb performance, more fuel consumption and major vibration on startup and shutdown.
The other model I've flown are a couple of Cessna 150/180 conversions that have similar comparisons.
In the case of the 150's, in addition to short field take off and climb performance, given the cleaner airframe, you get more cruise speed increase from the 180 HP than you do in the supercub.
In the case of the supercub with so much parasitic drag, there is little or no cruise improvement ... but short field take off and climb performance is better, but not so much to offset the extra weight, extra fuel consumption, and that infuriating vibration/shutter at start up and shutdown.
In my humble opinion the Cessna 150/150 and the Piper supercub 160 are the sweet spots. Pushing either to the 180 HP is overkill.
