Of course I might add that every light was green on my 27 mile commute today. Normally I would get about 30-31mpg...
I was thinking that Chicken... I do notice that after I get past 2500rpm with the A/C on, it gives a good whine. So maybe I'm low on freon. I will say that the 95 degree days we had, I turned it to #3 after about 10 minutes for the rest of the ride home, unless I was at a light and it started getting warm from lack of rpms....Can't speak to the GXP ghost, but my N/A ran 28-30 mpg on last summer's road trip, a mix of A/C on and off. (Same 1 mpg variance between on and off.)
The A/C compressor is a parasitic load, but it sounds like yours is a bigger parasite than most. Going bad perhaps? I don't know if there is a "torque" rating for how freely it should spin when engaged.
I notice a touch difference in performance, but nothing major. Of course mine is a GXP so the turbo makes up for the power loss. My issue is with my gas mileage!Since we're on the topic of A/C, I can't say I have noticed a drop in MPG, but the car does seem to perform differently with the A/C on. I know this can be the case in many cars, which is why when racing or driving spirited the A/C will typically be turned off, but do you notice this as well? The car is sluggish on acceleration and will bog down upon a normal start from 0, more so than normal.