Hi. I'm 6'4. on 63. I think it is not depending on how tall you are, but how long is your reach and how flexible your body is. Also for what you ride the bike. In this case you're clear that you want upright one. So my suggestion is to get 58 and put a longer front fork.(Might be a lil bit weird looking though...)

For seat post, You may be able to use longer one to adjust fitting, and it doesnt really matter as long as the very end of your seat post is located lower than where TT meets DT. (NEVER locate it higher than TT height.)

BTW, I like Wrench Science's fitting system. Chose either Road or MTB and you'll see "fitting system" in menu at the top. You may refer what size fits you and you can adjust from that.

http://www.wrenchscience.com