56 would probably be the right size for you. 58 would probably be on the marginally big side. Most people can be fit reasonably well on more than one size of bike frame. My guess is that a Nitto Technomic stem will give your 54 the extra handlebar height and reach that you want.

Regarding fitting 700c wheels - find somebody who will lend you a pair to try. In less than 5 minutes you'll know if you are going to have to change the brakes, or scrape a pedal on turns, or if the smaller wheels will make your bike look too goofy for words.