I think, for the current cost of the XS Max vs the sale price of the X, youre not getting much for your money. It's a lot of money for a phone that is overall a similar experience.
I'd be more encouraging if you were coming from an older phone
X is a very fast and capable phone. I have a X and XR (personal and work devices) and despite the A12 and LCD display, the performance between the two is identical in real world use.
X is a bit quicker in some areas because 3D touch is instant vs the haptic touch delay. But they feel identical in real world use. Heck I've sat there with my old 6s and done speed tests, and if the 6s is more or less identical in speed with opening most apps and navigating the UI as the XR, you bet the gap between the X and XR (A11 and A12) is razor, razor thin.
For the record, i used to own a XS Max and returned it, because I couldn't justify the price difference over the X. Like it just didn't make sense for me, I could have purchased a whole other brand new device with that money difference.
A note with the cameras, people online will make such a big deal about the smart hdr but take a pic of both with hdr and throw it on your computer and they look pretty much identical. The X is by no means a poor mans camera just because its a year old. People obsess about it too much, and get sucked into apples amazing marketing. Overall the phones (X and XS Max) feel similar In terms of experience.
I suppose it also depends what you value the most... If you value a larger screen above everything, then those hundreds of dollars to upgrade makes more sense. I just see it as throwing away hundreds of dollars, that could go to a more tangible upgrade in the future
I'm sure you are weighing in everyones opinion. Take time to read both sides and see which stance makes sense to you. I'm sure someone who has upgraded will have a convincing argument why it's a good idea!
It's your hard earned cash; Spend your money how you wish OP!