Golite stuff is either Goretex -- which is "highly breathable" in Goretex market literature but not in reality -- or Golite's own Alchemy -- which is even less breathable than Goretex.
I too have the SD Isotope. Nice cut and color, light as heck. I had the 2006 version which was a disaster. After complaining to SD's Warranty Dept., I got a 2007 replacement. It's more or less waterproof (much better than 2006 anyway) but just barely breathable. If you buy it, hike as slow as you can -- and don't hike uphill.
Some figures for comapison:
MontBell Particle - 15,000 g / m2 / 24 hrs
Goretex XCR - 13,000
Marmot Precip - 8,000 or 10,000
Alchemy - 8,000 or 10,000
SD Isotope - 3,000
What do those numbers really mean in real life? Beats me. But they at least serve an illustrative purpose when compared together.
Finally, my understanding is that eVENT -- being air permeable -- tends to be the most breathable, followed by MontBell Breeze Dry Tec, which is also air permeable. After that comes MontBell's wp/b coating, the various versions of Goretex, and then the various proprietary wp/b coatings in some descending order.
eVENT and Montbell Breeze Dry Tec lead the pack because they've managed to be rainproof without the need of a PU layer or coating, unlike all the rest.