If by working speeds you mean capacity, I would give the edge to the 7088. We have 2 7088s and a 7120. I don't see why you couldn't run it in 3rd gear, (the 7120 has 4 gears), but don't take my word on it.
in the 20 series combines 4 speed transmission most run in 3rd with smooth solid ground conditions maybe second in soft/hilly conditions my father has a 5088 and runs it in 2nd in the field[/quote]
Maybe we're different than others but we're running our 7010 in 2nd gear. We can run faster in 2nd than the combine can handle the corn so I see no need to run in 3rd.
In soft mud I have found the transmission / hydro tends to stall out in 2nd gear and won't spin the tires, especially with a 3/4 tank of grain or more. . In those kind of conditions I have been running 1st gear. Combine will still shell at about 4.5 mph and will have enough torque to spin the tires.