I had an 04 Series I, then traded for an 08 Series I head, which I ran since 2014.  I ran the 08 the past three seasons with Calmer stalk rolls.  Ended up trading towards then end of harvest for a 21 GT.  I pulled off the choppers a on the 08, a few years back, and installed Yetter Devastators.  I had a new set of Devastators installed on the GT head and like the job the do.  I like the upgrades that the GT has, which is no transfer gearboxes on each row, no chain drive gearboxes on each end of the head and no chain driven auger.  The GT has quad suspension deck plates and I think that makes a huge difference when harvesting really dry corn.  I had to look really hard to see any corn on the ground behind the GT head.  I am running the Drago stalk roll knives on the GT and was doing a nice job on the acres we finished upon. There is less in-season maintenance on the GT head, which is at the 20 hours and consists of 2 or 3 pumps on each gathering chain sprocket and one on the stalk roll.  Before each season, I usually have the head checked over by one of the techs.  I figure they can check it over and know what to look for and this almost eliminates in-season breakdowns.  I did have the input shaft bearings on my RH gearbox go out on a Sunday afternoon this fall.  A quick phone call to my Drago dealer verified the parts that I needed were in a parts depot that is 15 minutes away from me.  I grabbed some bolts that I needed from a local machine supply and was back going the next morning.  Drago does have a nice website with videos that show how to do repairs and there is a parts breakdown as well.  I am happy with the Drago heads over the years and really happy with the GT upgrade.