Leonard,

I own a C172 180hp, Airplains conversion, fixed prop. I trained in a
regular C172, 160hp. Handling is identical, from my experience. I
recently damaged my plane (taxiing, damage to wing) and have been back
to flying a 160hp rental while my plane is being worked on and having
some long range tanks being put in, so I do have a little experience
going back and forth.
Airspeed in the 180hp is a reliable 124 knots true, plus or minus 1 or
2 knots. I don't recall the airspeed now in the 160hp except that it
seems to be about 10-15 knots slower based on travel time to and fro
some familiar destinations. YMMV. Fuel burn in the 180hp is about 9.6
gph, but this varies from 9.1 to over 10 depending on length of flight,
climb/descent profile and practice. I flight plan 10gph to be safe.
The 10+ gph is on short flights where I climb up and cruise for only
about an hour. The longer the flight the better the gph, which makes
sense of course. Not sure about the fuel burn in the 160hp since I
rent it "wet" and don't pay too much attention since I haven't flown
more than an hour and a half one direction. (I do check the tanks using
the old wet finger method.)
Climb is definitely better in the 180hp, from my limited experience
probably 500fpm better. Since I live in the West, this is also nice
due to the occasional DA issues that can arise.
You can do the math on the range. At my home airport (BIL), alt 3550,
with full fuel, 2 people, and probably 100-150 lbs of stuff, I'm easily
off at 60-65 knots w/in 1500' w/o short field procedures, depending on
temp, etc.
Useful load is about 200 lbs better. Consult the specs.
Frankly, I wouldn't own a 172 with less. My plane is a true 4 person
plane, full fuel, plus 90 lbs left for stuff. 95% of my flying is just
me and the wife, so we can really load it up. That's why I'm adding 30
gals capacity to the 40 gal tanks. We'll be able to fly good IFR legs
with plenty of reserves. Of course I do need the portable pee bags now
for her.
Oil access door is more easily accessible, too, since it is over
towards the side rather than right on top like the 160hp.