Did you buy the 820 new?
Was there anything smaller than the 811 like in the 6-8 ton class
811 was the smallest, but you won’t find many, 812 was a bit more popular, but the model built in the biggest numbers was the 814. Non Super machines had different final drives , the Supers were far superior in the track department.
816,817 and 818 were also available. 817 was my first mount, a rare beast, even back in the day, sadly it lacked the “Super” spec, so wasn’t the best machine, but I have fond memories as it was my first full time mount.
We didn’t buy the 820 new, it was five years old, it will be 30 years old next year, with circa 18k hours, it’s coming into the yard for a full set of undercarriage and a full overhaul, planning to do it sometime over the next 6 months, but we have been saying that for several years! But she is very poorly now, so it really needs doing, it’s dads favourite machine, it’s hard to stop him driving it!
816 and above had bigger, heavier booms than the smaller ones, and a very different upper structure design, despite very similar looks from the outside.
Downside to the design was the sharing of the same sized slew ring throughout the range, which resulted in the smaller ones being almost over built in the slew and the bigger ones being a little under built by modern standards.
They also chose to retain the 2.5” pins throughout the range, the larger models had bigger main boom and dipper pivots, but had the same 2.5” pins everywhere else, which was ok on the 814 and below, but a little undersized by modern standards on the 816 and up.
I remember tales of a 822, iirc it was experimental and never made it into production, but that could have been just a myth? Be nice to know if it was true or not?
All models with variable pumps, had the same Rexroth AV80 pump, Super didn’t exclusively denote a variable pump, as the larger Non Super models still had the variable pump, but smaller Non Super models did have triple gang geared pumps.
.... running gear well buggered on that 
