That sounds nice in theory, but I think even at the best of times, false in practice - and the Leeds to Settle Jcn bit was not "newer" in any case (remember, PSRs at Shipley, Keighley, Skipton and Settle Jcn, and I've probably forgotten a few).
Nonetheless, it was, generally, a 90 mph railway, and - I'd need to check the trainling loads, but Appleby - Carlisle non-stop could be done with a Midland Compound in 30 mins non-stop. It was, of course, downhill almost all the way.
So, if you could life the line speed to even 80 mph, a limited stop 158 (Skipton - Settle - Appleby - Carlisle) should be able to do that stretch in, what, 90 (?) minutes instead of the current 120 with all stations. That would give you something like 2 hr 10 mins Leeds - Carlisle. Most trains take 2 hr 40 or so right now.