I have ridden both locations a number of times. I would suggest not bothering with the Nevis range uplift this weekend if the SDA is on. Even if the red run is open, it isn’t really worth it on it’s own and the lift might be busy.
I wouldn’t ride Glencoe DH if you’re having an off day. It is a lot more technical than fort bill even in the dry. If it’s wet then it’s way harder. If you enjoy steep and techy, you’ll love it.
I haven’t ridden the red run at Glencoe for 2 years. It was pretty dull then but it hadn’t been open long, I believe it has had a lot of work since but can’t comment.