Have you tried a shell with GoreTex XCR?? It is a step up in breathability over standard GoreTex. I sweat like a bastard in certain conditions. I find that my XCR shell can manage that quite well. If it's cooler than 35F, I have no sweat problems at all. In the 35-40F range, I sweat a little but the jacket ventilates well enough that it's not a continuous problem. Above 40-45F I switch to a windstopper fleece which breathes even better, but of course it's a mild weather (no precip) solution.
One thing I noticed about XCR is that it can "catch up" with the sweating and help you dry out. Normally, I sweat a lot while getting dressed in the morning and on the first 1-2 runs of the day. I think my body is figuring out it was indoors (warm) with clothes on and now I am exercising, then later on it adjusts to the outdoor temps. If I had built up some sweat/dampness in the initial dress-up routine and first few runs, it is generally gone within 10-15 minutes, meaning the jacket let it out and caught up with my body. With older, less breathable coats, they often never let the original moisture dry out and I'd have damp base layers all day.
I also skied in a stretchy softshell earlier in the season, and felt it breathed slightly better than the XCR. But honestly, I never was able to make a one-to-one comparison. About the only thing I can say strongly is that the XCR shell breathes impressively well for a waterproof jacket. In fact, it breathes better than most non-waterproof jackets I have owned in the past.