There will obviously be trade-off's to performance and it's so early right now that it's difficult to say what will change for all games. The S is still an impressive piece of kit for the price, and any enhancements to older games and the ability to play next gen at a lower resolution will be good for many people.
I was originally going to go for the X, but I ended up with an S on pre-order initially. I was annoyed with myself because I literally had an X in my basket at Amazon and talked myself out of it for reasons I don't even remember. I then placed the S order and instantly regretted it, but had lost out on the X stock at Amazon. I eventually managed to get one from Currys but I do feel that the delivery on Prime would have been better than what I'll be getting free with Currys. We'll have to wait and see! Not long now though and despite what many are saying (not here, on the Internet in general), I'm really excited to revisit games on Game Pass with a far better experience. I can't wait!