I love my Brooks on my distance bikes, but on my CX race bike I have a Selle Italia Diva gel flow. Similar wide flat profile as my Brooks, nice cutout, good padding for soaking up the bumps and such on a chattery CX course. I have a Specialized BG Henge Comp on my MTB. It's narrower, but since I spend less time actually sitting on it than I do standing and pedaling, it's no matter. When I do put my butt on it for a while, it's comfortable. I've also used a WTB Pure V, which worked well for me up to about 50 - 60 miles at a time.
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"I feel like my world was classier before I found cyclocross."
- Mandi M.