You figured it out, 58cm Stanyan can be a back breaker for a 6'3" rider. ES is pretty cool looking, I'd get the carbon fork too, or at least the lugged crown fork (since you're saving all that $$). I wouldn't be shy about going to the 60cm (nobody's getting younger). It will require a 20mm shorter stem to have the same position (reach) as your CAAD. The IRC forks are supposed to have 350mm steerer version, that's ideal for taller riders, I never see them in stock.