My two cents, I am also 5'11" and 175. I have a redfish king and it fits just about perfect, but it is a lot of boat. So, without having ever used a guillemot or petrel I will use my best educated guess. Guillemots are designed to be manueverable in wavy conditions, which can be common on big resevoirs, but it may not track as straight as you might want if you plan on long distances. I think they are one of the best looking designs. Petrels have more of a hard chine which would provide stability and add tracking ability. I think the petrel was designed for a pretty large person as well. It would be a good choice for rough conditions as well.