I'm with Beezers on this one. The pecs really aren't a big muscle group, so I think that doing a lot of sets is overkill. If you're looking to add size, 6-8 heavy working sets has always worked best for me (working, as in don't count warmup sets), in the 6-8 rep range. I've grown most from doing 3 sets of flat bench, 3 sets of incline D-bell presses, and 2 sets of heavy pec dec to finish. just make sure that you always have a spotter on the first two exercises, because the weight should be enough that you need a spot on the last rep...NEVER stop a set before you need help on the last rep!