I run 145/15's up front and 195/75/15's on the back all on stock 4.5\" wheels.

I went with the extra tall rears because I can't afford a freeway flyer tranny. With 165's I was winding out pretty good at about 65 mph. With the 195's I can cruise comfortably all day at 75 mph and not feel like I'm going to get knocked off the highway by an SUV, and I've still got a few extra rpm left over if I need to pass. I was a little concerned about the lower highway rpm causing the engine to run hotter (lower rpm = lower fan speed) but I haven't noticed any change.
As a side note, I have had the front end adjusted about 2\" lower than where it sits now with no tire/fender clearance issues with the 145's and the stock width k&l beam.