Prock, I really don't think there's any advantage to using both at the same time; they both basically work through the same mechanism. I'd say that Clomid is the stronger booster of endogenous test. I usually do something like this:
day 1: Clomid, 300 mg.
days2-14: Clomid, 150 mg.
day 15: Nolva, 80 mg.
days 16-28: Nolva, 40 mg.
This allows you to use both Clomid and Nolva, as there is still some controversy as to which one is superior for PCT. Also, as you're limiting use of each drug to two weeks you can use pretty high dosages with less chance for side effects.