I'd have to agree with ephman - let your body dictate your resting length between sets. Generally, my rest periods are shorter when I'm in the high rep range than when i'm in the 4-5's, for example. Also, some days are better than others, and you can always shorten your rest if you feel energetic and strong.
The important thing (for me, at least) is to start the set when I feel ready. If my rest is to short, I won't be able to reach my full capacity, and if it's to long I'm beginning to lose momentum.
Regards,
/R