I am intrigued by the RH Steilacoom, which is 38mm with knobs. I have been racing CX on 33mm tires for years but like the idea of running a wider knobby (but not MTB wide). My only hesitation is that RH tires are really expensive and we see a fair amount of mud in my series (see post above), so I think I'd still need a 33mm mud tire as well, and that PDX happens to make a really good all-around tire. I don't really want to be switching out tires all the time during the season.
I see guys running MTB's, fat gravel tires and even fat bikes at all of our races. Most of the time these guys are just messing around and not competitive, but some are really fast. I don't think the wider tires are really providing a significant advantage - in some areas sure, but they're probably slowing them down in other areas. I think it mostly comes down to the motor.