Petsafe ULTIMATE v Classic Cat Door (4.25" wide enough?)

I am going to get a cat door installed in near future.
Appreciating all the feedback a few months ago,
I am trying to decide between these two models:

Petsafe Ultimate (Small): opening 4.25" x 7"
Petsafe Classic (Small): opening 5" x 7"

The Ultimate costs a bit more and I am sure it is better
quality in many respects (although classic may be good
enough). I am just worried about the 4.25" opening.
Is that wide enough for most cats in your experience?

I know that cats can squeeze into spaces you'd not have
thought possible, but as a novice I would be reassured to
hear from someone more experienced.

(I don't want to go too much by my present visitor,
who will probably squeeze in. The installation will be
long term and someday we may get, or get visited by
other cats too. However we are not thinking dogs.)