I was in the same boat December last year. No X01 Spurs in stock with my local Transition dealer and they said none coming until 2023 at the earliest. They had one large GX Spur so I took that. Best descision I ever made.
GX spec Spur has lower spec forks and shock too
The differences are negligable. The only difference between the Sidluxe Ultimate and Sidluxe Select+ rear shock is that the air can on the Ultimate has a tiny bit more CNC machining which loses an extra ten grammes of weight.
The SID Select+ I’d argue is actually better than the SID Ultimate for trail use because you get the full size damper rather than the strpped back Race Day one. I’d rather take the 150 gramme hit and have a fork that is actually more plush than the Ultimate. Also, the SID Select+ has a proper adjuster for the rebound and not that tiny allen key thing.
I used the £1,000 I saved going with the GX model to buy some nice carbon wheels. I’ll upgrade the GX stuff to X01 as and when things wear out but I’m 1,400 miles into the stock chain and stil haven’t hit 0.5% wear according to my Unior chain checker.