I believe the geometry of the WC Kruis is the same as WC Opafiets. WC can verify this for you. At one time the top tube was necessary for frame stability for larger (male) riders and the Kruis was an option to provide the same stability with a slightly lower effective top tube height — for pastor's garments. Today the top tube or double top tube or kruis is often more tradition than necessity except for really heavy loads. Most males can ride a step-thru or Omafiets with no problems.

The WC SS is slightly more aggressive and stiffer compared to the Opafiets (or Kruis?). My personal preference is an Opafiets or Omafiets over SS but I also know people who prefer the SS.

More: City Bikes | LocalMile

My personal preference is front roller and rear coaster. Partially because I like to be able to brake when my hands are busy otherwise and to avoid any problems with frozen cables which may not be an issue in Oz. My wife prefers front & rear roller because she likes to be able to spin her pedals backwards to get them set to go again at junctions (but her Oma at our cabin is coaster and she never has any problems).

I have a Nexus 8 on one bike and Nuvinci N360 on another. I do prefer the Nuvinci but both work well. Whatever you choose I think you'll be happy with a Workcycles.