Take your time, don't listen to any bollocks like "you look like you'll need an extra large frame". If they don't have the bike in stock they will be able to get it for you. This does not reduce your buying options.
I am 5'11" and the bike I ride has a 56cm frame, not because I'm 5'11" but because that's what fits me, you need to understand more about reach, inside leg and the like to get a true fit but in essence you will find many bikes that will suit you. Is this a road bike that you are looking for? If so then disc brakes will be an unnecessary additional cost, I don't know enough about mountain bikes to give advice on those.
EDIT: just looked back and you're looking for a road bike, disc will be a waste of your money.