This website is probably the best fanfiction/hypothetical ever for the Trek pre-TOS period. If you like to see a well reasoned out pre-TOS ship designs, or just simply curious as to how they should look you must come here. You will be surprised that they look pretty well. The designs look simply, clean realistic and possess a strong retro-charm to them. The ships also have interesting stories and backgrounds with reasonable analysis of their tactics, weapons and techs used. Ships here range from the time of First Contact to just before TOS, and includes combatants of the Romulan-Earth war. I certainly think this is the best pre-TOS website.
http://www.ex-astris-scientia.org/sfmuseum/index.htm