I have a few WORCS races in with some MX also, I run the Big horn 2.0 on the rear (26"). I like them and run the 9" wide on a 7" wide wheel, I like this set up because its light. Plenty of traction with a 1000lb utv.
I just started running the 26" MAXXIS 4 speeds on the front, I'm happy with them. Again, there light. I dont see any reason to run such an aggresive tire (bighorn) on the front of my RZR. The regular big horns are boat anchors.