Um, are you going to edit the thread title? Sorry, I'm feeling 12 years old today.
Oh, guess I should say that size 7s for cascade fixation will result in a holey and loose sock, unless you knit really tight, in which case following the pattern, which probably won't be made expecting to be knitting extra super tight, will result in too loose a sock. Even socks for worsted weight yarns, which are generally heavier than Fixation, usually go down to a size 5 since socks should be made at a tight gauge because they receive lots of wear. but you can try this page:
For what it's worth, I knit Fixation or that type yarn for socks on size 3 needles.