XTR M952 Short Cage - Maximum Rear tooth capacity

[Retrorockit]

looks a little short to my eye
I guess I don't like the RD to be that stretched out

but presumably this is on a 1x drive train right?

Yes this is the mid drive Ebike. But it's my 2004 Gary Fisher so Retro stuff lives on. Like Avid BB7s. Rapid Rise, and Revoshifter. FFW too.
The 33t total capacity RD leaves a little play at each end with the 29t range cassette. This is ridden long and hard daily. It even works under water.
This also has a Front Freewheel Mod. The cassette turns any time the wheel is turning. Sort of like an 8 speed fixie. I think I posted a video of that earlier. I had a longer derailleur hanger at one time, but the B screw is all that's actually needed.

 

[Retrorockit]

looks a little short to my eye
I guess I don't like the RD to be that stretched out

You may be right to some extent. With the zip tie mod to (softly) lock out the rear freewheel, if it needed to throw some slack into the top run of the chain downshifting at high speeds it would snap the breakaway zip tie even though it's supposed to just be there as a fail safe in case the chain gets hung up. I put a greased rubber ring between the hub flange and the cassette instead, now it just slips a bit if it gets too tight. I don't think with out the FFW mod there would have been anything to notice. The normal freewheel action can't push slack into top of the chain to begin with.
But in this extreme appplication it does run out of travel every now and then. but I routinely throw it into low gear at 20mph in anticipation of a stop in traffic, and nothing bad happens. If there's enough travel for an extra link in the chain I would say do it. A new cassette should have a new chain anyway. Just work your way down to something useful.
Just Rapid Rise was easier on things. You just fed cable into it while slowing down w/o pedaling but the shift didn't actually happen until you pedaled it into gear just before stopping, the freewheel was still active.. But FFW is real time shifting up or down pedaling or not. RR can still downshift when stopped. I'm having a lot of fun with this old school junk in a modern application. But when I say this has been stress tested I mean it.