>When the values are sorted (modulo empties and wrapping) you don't need to store the probe length. You just maintain the invariant that things are sorted. Maybe I'm missing some detail of your implementation, but mine sure don't bother storing it.

Storing the probe count allows the lookup function to have 2 branches per loop as opposed to 3. The probe count also contains enough information to distinguish occupied buckets from unoccupied ones. I'm convinced that combining the probe count with the hash is objectively the best way to implement such tables.