I went from a Series I to a non-chopping GT towards the end of fall.  I couldn’t believe how much less head shelling there was with the GT.  Going to the GT head will eliminate transfer gearboxes on every row, chain cases at each end of the head and chain driven auger.  You get a larger diameter auger and better transition from the auger to the feeder chain.  I gained gas struts on each snout, rather than the support rod that my Series I had.  There is less maintenance required on the GT head.