Your comparing apples and oranges with different models.
There is also tire diameter and front and rear sprockets to consider.
In 87 Honda changed the 2 mating gears for 3rd gear just to change the ratio a hair. The result is basically a cracked 3rd gear in every 87 motor I own. But thats Honda, striving for perfection.....
As for comparing the 2 Tri-Z's - the manual should give you all the gear ratios. Sometimes the top gear puts about about the same ratio be it 5th gear or 6th gear in different motors, but all the gears between are just a bit closer and offer you more range.
Remember the 4 speed YZ490?? I guess when you have 500CC of pure 2 stroke madness, it doesn't really need allot of gear choices
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country