150? thats a bit extreme. I'd shoot for anywhere from 12-16 reps within 3-5 sets. Use enough weight so that you do feel resistance, but not enough weight that you're struggling to get the weight up. While toning you'll probably also gain more muscle in the process.
I've noticed that my gains have been faster doing it this way, but I'm in no way getting stronger as fast as I was when I was using heavy weight/less reps. I did that 3 years ago and look wise I didn't change much, but I was much much stronger. Now this time around (got out of the loops for a while) I'm doing less weight and more reps and noticing I'm getting bigger and more cut, but not getting nearly as strong as I was. It's all up to what you want out of your body.