I've also been an X-fan for years and strangely enough only came across the Whilce Portacio part on the right some months ago for the first time, whereas I'd seen the Jim Lee piece before. Didn't realize circulation was so scarce!
I wonder what Claremont's plans for Guido might have been as I don't believe he ever mentioned anything in interviews. And while I think that Jim Lee roster is pretty strong, the "X-Factor plus Gambit" Portacio Uncanny X-Men doesn't exactly excite me. Still, it was 90s Claremont paired with Lee and Portacio at the top of their game, they could have produced toilet paper and I would probably have enjoyed it.
Regarding Legion... Peter David could probably have done wonders with him on X-Factor, he might have been a bit of an odd fit but then again he had established relationships with Jamie and Lorna at least, so he might not have been totally out of place.