I’m between 5’11” and 6’ and am happily on a Large. I ordered it through my long time bike shop after trying out a higher end Creo in Large at their place. The owner and I had several discussions about the size I should order - he was leaning towards an XL, but I felt right on the Large. Never got on an XL and still haven’t.
I hesitate to enter this discussion at all, since this has to be your decision to live with, but I will note that I just checked the Geometry section on the Specialized website for the Creos, and I note there are some pretty significant differences in several areas between these sizes. The Reach and Standover heights, among others, tell me that I definitely made the right choice for me.
I wonder, are you a guy who likes to be sort of stretched out to the bars or more sort of gathered together? I go with the latter, and I do particularly like the fact that the top tube is somewhat low and the bike just overall easy and comfortable to negotiate. A younger, more aggressive type might want that larger frame under them. It’s all so subjective!
Where are you in the US? Maybe somebody here has an XL and ain’t that far away from you… or, for this kind of expenditure I would consider a pretty good drive distance to go find one at a shop.
Oh, and by the way, after 14 months and 3400 miles, I remain convinced that the Creo is the best bike I ever owned, and I’ve had a few over the last sixty years or so.