If you get the 17.5, make sure the seatpost is long enough. Riding with the post over max height could ruin the frame.

I am 5'9" and require an extra long post on a 18" frame, and my legs are not particularly long.

One option is the longer bike with a shorter stem. The 19 with a 70mm stem is probably exactly the same length as the 17.5 with the 100mm. In my opinion the long top tube-short stem combination is a nice handling set up.

Frankly though like a lot of folks you probably want the 18 they don't make any more.