"Can even the best rain shell actually keep you dry?"
I'd say that because of the speeds at which you normally hike, you're going to sweat regardless, so you're going to be wet. At least the rain jacket will help keep you warm. If you felt the 150 wasn't quite enough, bump it up to a 200 under the same conditions next time.
I don't know if y'all took a mid-day break for lunch, but on such a day I'd skip the break, as you'll just cool down quickly and you won't really want to drag out an insulating layer in the pouring rain. Keep moving until you decide to set up camp. At least then you'll maintain temperature throughout the day. Then get into dry clothes for the evening!
A day like you must have had last Saturday would have been a perfect day for my eVent Packa, I think....
Also, make sure your feet and hands are staying warm/not cold. Get your feet and hands cold and the rest of you is going to feel cold (but you know that already!).
In short, at your speeds/exertion level you're gonna be wet no matter what - either from rain or from sweat. It's the staying warm part that's important, as you know. I think the Icebreaker 200 might have worked a bit better, along with, perhaps, a waterproof shell on your hands and feet.