If you run regular dinosaur oil, I wouldn't go any more than 3,000 per change. After that far, it starts breaking down and sludging up and you can't get all that junk out of there no matter how often you change it.
Now if you run part or fully synthetic, I think 7,500 is entirely within reason. Good synthetic oils have been tested up to 10k+ miles with little to no breakdown. You pay more for the oil, but you don't have to change nearly as often.
Whatever you use, just get the quality stuff. I recommend doing it yourself since I've heard so many horror stories with quicky change oil places. But if you can't, at least WATCH them as they put the oil in, so at least you know you are getting what you paid for. If they give you issues about being in view of the change while its happening, go somewhere else.
One other thing, I highly recommend getting an oil filter with anti-backflow valve if available. It keeps the oil in the upper engine from draining back though the filter and into the pan while the car is sitting, and reduces start-up damage. Most of the wear and tear on a engine is right after it starts.