Cuben is somewhat vulnerable to abrasion and punctures. It's fine for tents and tarps (especially the latter) if you can afford the price. For rain pants, especially, you're going to be vulnerable to snags every time you have to crawl over a deadfall. The hybrid cuben that ZPacks uses is definitely less vulnerable (I have a couple of pouches made out of it), but it's pricey.

Frog Toggs rain pants are fragile and DriDucks (cheaper version of the same fabric) even more so. My Frogg Toggs pants sprouted a lot of duct tape patches and became too abraded in the knees and seat after half a dozen trips. I've seen a lot of reports of DriDucks pants splitting from stem to stern. Since breathability is not all that important in rain pants, I'd suggest silnylon.

On the other hand, my Frogg Toggs jacket combined more breathability with more waterproofness than any other "breathable" materials I've tried. Admittedly, my experience with it was 8 years ago. The jacket lasted three years (including a lot of around town use) with only one duct tape patch (and that was for a hole from a bonfire spark). By that time it was abraded enough to let in heavy rain. Frogg Toggs are low enough in price that you can buy several sets for the price of one pricey "breathable" jacket. Just ditch the pants which, as mentioned, don't hold up.

My experience with the expensive "breathable" fabrics such as Goretex and eVent is that, at least for me, they aren't all that breathable. I get just as sweaty inside them, if not more so, as I do with a loosely cut rain jacket of just plain silnylon for less than half the price. Your Mileage, of course, May Vary.

My latest experience with "breathable" fabrics was a Marmot Precip jacket that "wet out" after a year. It continued to do so even after I did all the recommended things to restore it. It's fine for walking from car to store through the parking lot, but for even half an hour's hiking in the rain, forget it.