What rig geometery would favor a frac rig (remembering the issue of jib
head tip vortex)?

in the context of jib tip vortices, a masthead rig would be better.

Would aspect ratio be significant (again, just a
reminder, jib head tip vortex)?

Of course.

How about the head angle of each sail
respectively?

WTF are you talking about?

dougies, give it up for the cripes sakes. you read a single article by a
numskull about vortices and now you are trying to play expert. Go read a few
dozen more books. A good start would be check a few of the books offered by
the EAA, mostly decent books written for the amateur.