How many spokes would you want on an Enve 1.25 front wheel, when the goal is doing fast alpine descents (also in races and sportives)? Rider is between 75 and 80kg, giving a "system weight" of around 90kg?
I just had a pair built up in April and rode them from mid-April to May 25 this year. I am slightly above your weight range at 82kg, but in my 20 or so years of riding, I tend to not be overly tough on equipment historically. So I think I'm a fair comparison for your question.
Because I wanted my 1.25s to be true alpine mountain wheels, upon consulting with the guys at Wheelbuilder.com, I went with 24 spokes for the front and 28 in the rear. These wheels took me up and down Mt. Baldy (and the rest of the >11K ft of climbing and descending that day) during the 2012 L'Etape du California, and they were absolutely rock-solid steady at speed. Sure, I have no doubt that I would have made it up and down the mountains on a 20/24 set with no problems, but for me, I quite consciously made the decision that I would trade 20g per wheel in order to have that added measure of confidence when high-speed descending and pushing it in corners. I should also mention that I went with an Alchemy ELF front hub because it features nice and wide hub flanges for a really strong wheel (the fact that is runs about 67g didn't hurt either). I have no doubt that for me at least, having complete and total confidence in my wheels more that made up for the miniscule performance difference that comes with losing 20g per wheel - making these the fastest alpine wheels for me (YMMV).
Mine have just done up for sale but only because I needed to switch from PowerTap (my rear is built around a G3 hub) to an SRM - this is in no way a comment on how these wheels perform - for their purpose (serious climbing and descending, with zero crosswind issues), these score a 10 out of 10. You will really enjoy them.