which model fks?
the fks pivot model, which is the same as look only plastic, is more expensive then the look, which is dumb to me, most likely you do not need an 18 din binding, nor does anyone really. but i still cant beleave that that is the only metal binding in the pivot, which is ok because it has a ten din range, and i fit in there (I am a 10) you can get a general idea for your din on like din setting.com just google din chart and you will get it.
if your lazy im 5'11''-6' and 180 lbs. that doesnt include ski gear. and level 3, so you could get an idea if you are going to be above or below that.
if you need less then an 8 din then the p18's are out of the question and then you dont really have the need for a metal binding, and seeing that you are skiing on 175 jj's you are probably not that tall so, the fks pivot 14 should fit you well.
this doesnt rule out the sth though, the driver toe is very good, but that binding is super plasticy.