There are many people your size (weight) in the FSX (wide shell), which is for a high volume foot. The spring (flex spring) can be changed (replaced) for a stiffer flex. You might need the #5 flex spring if you were fit in the FSX. The FSX flex spring is also a ski walk mechanism which was designed into the boot back in the 1960's when some people used the Strolz for ski mountaineering so you could relax the forward lean for hiking or skinning uphill. I have been skiing on the classic shell with the springs since the mid 1990's. I am not sure what issues you speak of, the main thing is to have the flex spring, ski/walk devise looked at every few years to make sure it is functioning properly.
Tim, the main boot fitter and manager of the Strolz in Hampton, NH can re-last the SST shell to accomidate wide feet, plus he uses the wide liner if needed. Without seeing your foot this is all speculation, however since you say you have a narrow ankle, the SST (or SWM) may work. The SWM, is the same boot as the SST but has a wide cuff option and should be able to accomidate your large calves. http://www.strolzskiboots.com/model-info.html
Please contact me directly, or Tim, if you want to discuss your options in more detail.