I have a star that's about 3" wide on my shoulder. It didn't hurt but then the nerve endings aren't as close together there as elsewhere. I've heard that upper chest, abdomen, spine, ankles/feet and hands are the worst. But I only have the one on my shoulder so I couldn't swear to it. Like I said, that wasn't bad. I didn't even mind the whine of the tattoo gun. It's a lot lower in pitch than a dentist drill so I'm not sure that comparison is apt. I was worried that the wiping they have to do to clear the area of excess ink and blood would hurt (paper towel on raw skin) but they coat the area in vaseline (or a vaseline type substance) while they're working so that's actually not a problem.
I would stress that you should ask to see your artist's portfolio. Also, be aware that if your tat is on a bendy spot, you're going to have to not bend that spot a whole lot until the scabs come off. I have a couple of tiny clean lines cutting into my star because I reached up to take a box off a high shelf. It can be fixed but it's still a bummer.