mic
Guest
We don't run a 6620, but have a 7700 and 9500.  We run a 220 on the 7700 and a 925 on the 9500.  Both machines could take larger heads, but mobility becomes a concern.  The 220 is the best for running down the road with the header on.  We move the 925 on a header cart.  The smaller head saves the time of dropping the head on a cart, then towing it along.  I would guess that a 20 foot head would go good on the 6620.  I personally would not go larger though.  Especially if you have the chance of running in tough conditions (weeds, green material, etc...)  You could definately plug up the cylinder in a 6620 with a 20 foot head.
 