The X has more storage (which is a really big deal, the way so many games are going digital), has the disc slot (better for buying cheaper games down the road) and is substantially more powerful (meaning shorter load times and better graphics). The load times are a huge consideration—once you try a Series X, everything else seems painfully slow.

They're on sale today, too ($400 seems to be the going rate). Better experience today, and more "future proof" for tomorrow.