The Perf Century isn't the only short Performance sells that has wanky sizing. The Performance Elite is basically the same sizing. I've always used XL shorts for the last 18 years so last year I got two XL Elites.

IMPORTANT NOTE: Don't ride with shorts that are too small in the Tool Box (if you know what I mean). It did a way nasty number (involving a pinch that gave me a blood blister) on my junk. Way-way-way not good.

I got an XXL Elite and sure enough the frigg'n leg elastic is about 1/2 inch too big while the rest fits just fine.

I can't buy performance shorts - their sizes aren't for humans.