Maybe not what you want to hear, but I've used Corbin seats on my last three bikes, and I think they're great. 600 mile day? No problem. I don't have any experience withthe Sargent or Gel seats you mentioned, but I've ordered 3 Corbins, sent 2 back to be reupholstered after the original covers wore through ( About 60 - 75k miles) and always got my seats back done well, on time, and for the amount quoted. No complaints from me about their service.