I go for the 47" or whatever is longest in the small sizes for 2 @ time MLing. I'd rather have extra cable than not enough. However, having way too much cable is a pain. The only reason I don't use 2 cics is that I have a tendency to knit with the wrong needle and that can be a real pain to straighten out. Oh, one other thing, the bent ergonomic circs aren't good for 2 @ time MLing IMHO because the bend makes moving the stitches harder and adds to laddering. I'll use my Chaiogoo Reds for other things. The Chaiogoo cable is less flexible than my Options cables.
I've been looking at yarn at Knit Picks. In their sock yarn they have Comfy fingering, a cotton/acrylic blend. The video they have for it says they don't recommend it for socks. Go figure. I want cotton sock yarn and think finding something suitable will be difficult.
I should never overestimate my basic arithmetic skills.