Thanks everyone for all the good info so far.

I had not really considered the possibility of zipper failure but I will take that into consideration. Although, I have yet to ever have any zipper, on panniers or cloths, fail on me. I have had a number of plastic buckles like the ones on the top loaders break though.

As far as keeping things dry goes, I have noticed that almost everyone with Ortliebs need some sort of system of plastic garbage bags, grocery bags, or dry bags to organize their huge main compartments. If you are going to cover all of your stuff with plastic anyways then why pay the weight, price, and in my opinion, ugliness factors of Ortliebs?

So far I am still really liking the idea of the P-400 panel loaders unless anyone has any other disadvantages that I have yet to take into account? I really like the idea of being able to get at my gear in the pannier without having to remove everything that is on top of my rear rack, a major pain in the neck with my current top-loaders!

To the poster who owns the p-99's, do they have enough capacity? Since I am going with the smaller p-400 instead of the larger p-500 I was thinking that I would compensate with larger front panniers. Thoughts?

Thanks again!