In my old 4.7L HO Jeep the A/C compressor was such a small load on the V8 you never noticed it. Now in my 1.8L Integra I can feel and hear each time the compressor clutch locks. Do a tank with A/C and one without keeping other variables the same and see how your car handles it.
In a cross-country road trip in my 2006 Jeep Grand Cherokee (the trip was in July 2008), driving across the northern states and into Canada, the temps were cooler and we didn't need to use A/C. On the return trip, we drove down the East Coast and across the southern states where it was very hot and humid, so we were using A/C all the time. When I calculated my fuel economy, there was a noticeable 2-3 MPG drop when the A/C was on vice when it was off.