I just bought my used first Sportster and LOVE IT! It is not just a girls bike (even though I am a WOMAN), and it has great power. I have been on the freeway with it a few times and keep up with traffic at 65 with no problem.
I put the bigger tank on it and I will tell you, I hear how the guys with the big bikes crab about the gas mileage on their big bikes and I laugh, because I get GREAT gas mileage on mine!
Good luck -- I bought my Sportster on Craig's List and got a 883, with 11,000 miles on it for $2500 and not a (darn)thing wrong with it. It was well kept up with mechanically by the previous owners. I bought the new tank (4 gallon) on Ebay and now I can ride 140 miles without having to worry about filling up! Can't say that for the BIG bikes. Ahahaha