I had a 503 and it didn't have quicktach.  It was about a days job to change from corn to beans.  
I could combine 150 bu. corn at about 1.75 to 2 mph.  I put an 8" extension on the hopper so I could get across the field and I broke the bolts off in the right drive wheel.  I replaced them and broke them again.  So I drilled out the holes and put in much bigger bolts and broke the axel.

It was really hot combining beans and really cold combining corn.  I used to sit in the cab with snowmobile boots, insulated coveralls and two pair of gloves to keep warm while combining corn.

The last year I had it we had some down corn.  In the rest of the field yield was 170 and in the down corn it was 150.  My neighbor had a 6600 Deere and he loaned it to me for the down corn.  Using the "new" Deere the yield was back up to 170.  I traded the next fall when the axel broke again in the middle of the field.