As a very pleased owner of a P172D (successor to the 175) with an Avcon Lycoming O-360 conversion, and after flying umpty ump 172s of all years from late 50s through some of the last ones made before the line was stopped in the 90s, I can give you a few hints on performance. I've had mine for about 15 years and 900+ hours. Yup, climbs a lot better. Yup, cruises slightly faster (I flight plan for 115 knots). Yup, increases service ceiling by about 1000'. Yup, it's not as smooth as an O-300 Continental. Yup, it burns more gas (I average 9.8 gph).
Now let's compare it to a 182. Nope, it doesn't climb as well. Nope, it's not as fast. Nope, it doesn't have the service ceiling. Yup, it's more economical to fly (9.8 vs 13 gph) and maintain (4 cylinders vs. 6, longer TBO). And certainly, nope, it can't haul the same load.
Part of what I like about my P172D is that it's fun to fly. Heavier airplanes are OK, but not as much fun. Is that an issue? For me, yes. Mine already had the 52 gallon tanks common to 175s and P172Ds, and that extra fuel burn is an issue for stock 172 tanks--36 gallons?
I'd suggest, as others have, that economically, it's a whole lot better to find one that has already been converted. Otherwise, it's an expensive conversion no matter which one you choose, and it's a time consuming one as well. It's a bit like avionics--find an airplane already equipped the way you want it, instead of equipping it that way after you've bought it.
Cary