Terry,
You have much more experience with big engine mods than do I - and I like your "sweet spot" analogy - it resonates well with me in a number of airplanes.
I have zero data on stability and control and handling on the 180/150 I flew. I just came away from the airplane not liking it - and I've flown a lot of funky machines, including the O1-E Bird Dog which would ground loop if you looked at it cross-eyed, the Cessna 411 which had the most incredibly nicely harmonized controls you could imagine but systems quirks that would drive you nuts and the Republic Seabee that was a true pussycat on the water and demanded firm handling on the ground. At the same time, I've flown a few airplanes that had big power upgrades and some accepted the process well and some didn't. The J-3 went from 35 HP to 150 HP without much problem. The Cessna 340 to the 340A had only about a 25 HP boost a side and it had all sorts of issues, including a harmonic vibration that cracked the horizontal stabilizers and required fleet-wide replacement. Riley put big turboprops on the Cessna 421 and created a mess - when Cessna did the conversion of the 421 to the turboprop 425 it required major changes to the airframe, including a nearly completely designed emmpenage, to absorb the extra horsepower and different vibration environment.
With all that as background and having flown four or five different and distinct types of airplanes over the years, the particular 180 HP 150 was one of the few that I didn't particularly care for in terms of handling and overall behavior. Again - it may have been the conversion, but I've flown a bunch of funky airplanes and I look forward to flying them again (just spent last Saturday giving dual in a 180 HP Cessna 172 on floats out of Mill Valley/Sausalito, California in big time weird wind, water, fog and noise abatement conditions - and doing pylon turns on the north tower of the Golden Gate Bridge and then Alcatraz Island) but if I never fly that particular 180 HP 150 again, I won't miss it. It seemed to be a meat axe conversion where a scalpel would have been appropriate.
I only have experience in one, count 'em, one, airplane with that mod. And it may have been a bad example. By the same token, I've flown some other birds that I was honored to fly, but had no desire to fly on a day-to-day basis because they were a handful to control. I purely love the Cessna Airmaster, but with that tiny vertical stab, it is neutral to negatively stable in yaw and I am never sure where it's going in a speed band between about 15 to 30 MPH on rollout and I don't trust the expander tube brakes. By the same token, the C17 Beech Staggerwing with the little Jacobs engine of the same vintage is a pussycat on the ground - pure Beechcraft handling and no issue of keeping it straight. Five years after the Airmaster, Dwayne Wallace and Cessna created the Bobcat which is a horrible pain in the whatsis to taxi, but an utter delight on takeoff and landing - and can be landed incredibly short by spiking it onto the mains and standing on the brakes because it will not nose over. (That took a little getting used to - I learned that it was used to train B-17 crews in the same technique as a solid wheel landing and max braking with the weight on the wheels would bring that four-engine pussycat to a stunningly short stop.)
So - basic aerdynamics says more horespower is destabilizing. From my point of view as the loose nut on the stick - 80% more HP on the 150 frame might just be a little too destabilizing for the unmodified airframe. It's not a nice airplane to fly other than for its design goal of towing gliders.
And I agree - I may have been flying a crummy mod, and your mileage my vary, but for that kind of power and money, one deserves a more comfortable cabin, good handling in flight and nice manners on the ground. The 180/150 I flew had none of the above - with that as background I'll take a Bellanca Scout or Aviat Husky any time.
With all due respect,
Rick
