I used to run a set of nobby nics for the shit stuff, and racing ralphs for the dry stuff, or a front nobby nic with a rear racing ralph if it was borderline, back when I used to race. Can't fault them, but nobby nics are slow in the dry, and racing ralphs get squirmy in the mud. I can't remember what sizes I was running, but I always preferred a fatter front and thinner rear tyre. The thin side-wall version is also worth the extra cash if you run decent pressures and you care about rolling weight.