Muddy loins

Ah great, I hoped one of the cyclocross heads would turn up!

I've been looking at the Avid Ultimates, you'd say they're worth it? They'd work fine with the s500 levers?
If I was looking at a slightly cheaper option, 40-50 is there good options? or should I just go for the extra 20-30 quid?

Plan is to build it up slowly over the next few months and yes, lungs allowing, race muddy hell and hopefully a few more cx races.

In terms of performance and ease of set up then I think they are by far the best cantilevers on the market. Setting them up takes time to begin with but once you know the order of things it's dead easy to adjust them. They offer good modulation and, if you grab a hand full of lever, they offer enough power to stop quickly. I'd run mine full time on my cross bike if it didn't have to double up as the child carrying bike (the rack fouls them).

The CX9s are good too, but aren't quite as powerful.

I've also tried Euro-Xs and Frog Legs and both are a massive pain in the arse to set up and don't offer anywhere near the modulation or power of the other two.