I am 5' 8 300 lbs what size road bike frame is good for me?

With road bikes it is not as easy as just going by height, as these bikes are very important to have properly fit. A very basic road bike fit, or "sizing", includes taking measurements of your inseam, torso length, arm length, and flexibility (I've been fitting for over 2 years and have never once asked someone's height). In addition, a lot of people measure slightly between sizes, and the bike of your choosing may need a little bit of parts swapping to actually dial in your fit and riding position... ie minor stem length changes, different drop to the handlebars, fore and aft saddle adjustment, etc. I would highly suggest going into a local shop to have them fit you