Welcome to the new and improved Proflex / K2 Tech Forum!
Are you thinking a longer stem and slide the seat back a touch?OP
I'm 5' 10'' and ride an Oz medium & XP-X Medium & they're perfect for me, but it will depend on length of legs vs arms etc. I tried a 171/2 inch Genesis & it felt miles too small, but the OZ large would be too big because of the reach.Just checked sticker, 18'' - that is a medium, right?