My AC always feels the same.. A small but noticeable loss in power. I counteract that loss of power by revving the engine out a little bit more, maybe 2 or 3 hundred RPM before shifting if I want to accelerate at the same speed. (5 speed) I have the 100,000 mile Subaru Super Blue coolant so I won't be changing it anytime soon- I have 30,000 miles on my car.