You can basically make the Flashman at 85 tons with about the same capability anyways :D IMO the "assault" class would have been better defined as 90-100 tons, since that's the weight range where 4/6 movement just doesn't make sense any more.
Would you have made a separate class for 80-85 ton mechs distinct from heavies & assaults?
No, they'd be heavies. Maybe bump "medium" up to include 60-tonners, as they work well for 5/8 movement.
Interestingly, if you look at the various "ability ranges" for lack of a better term based on movement profile a mech breakdown would look more like this.
20-25 = Super Light (Can't do what a 30 tonner can)
30-40 = Light (Best Option for 7+ movers)
45-60 = Medium (6/9 to 5/8 Brackets w/ Moderate firepower)
65-85 = Heavy (Standard 4/6 Movers w/ Good Firepower)
90-100 = Assault (3/5 only w/ Heavy Firepower)
Though in the end, I think the 20 ton brackets works just fine, I kind of like the fact that 55 is more efficient than 60, while 65 is the least effective tonnage in the game, it creates "flavor" & variety.
Its nice to take those unoptimized designs and use them to abuse you opponent who is only using the "best" mechs.