I just fitted an SRAM S7 on my geared (vertical dropout) On-one Inbred and though I bought a chain tensioner I've been lucky with the chainring/sprocket combination and I don't even need to use it. From my trawling around on the internet it certainly seemed that the S7 is both functionally better than the shimano hubs and just a bit more durable/reliable. The standard S7 is 130mm, the hub with brake is 135mm. So far so good with the S7 - even did a bit of touring round the Yorkshire Dales last week and it worked absolutely faultlessly.

It was pretty expensive to retrofit the hub though. If its the shimano hub you really want why not invest in a Carrera Subway 8 or a Ridgeback Neutron or Nemesis? Or get yourself a lovely On-one Inbred frame with sliding dropouts and build a new bike?