My actual bike is a 19" 27.5er frame, but the top tube is short for the size and have a effective top tube of 595mm and a reach of 415mm, actually have a 100mm stem, and the distance of bottom bracket center to top of the saddle is 71.5cm. (inseam*0.88)

 I compared the geometry, and the M062 frame in 17" is almost same in lenght of efective top tube and reach, only I dude in the seat tube, years ago I had a 17" frame and broken in the seat clamp zone after 3000km (Marin Team Issue) but I dont know caused the seat post, use a 27.5 wheels in a 26" frame or a material fatigue. if I choose the 18.5" I need a 80 or 90mm stem I think.

Photos of my actual 19" 27.5" frame, and my old Marin 17" with 27.5 wheels

I listen opinions to decide.

Greetings