This is the type of thinking that flaws this whole issue. Any time a person says about using a heavier DW someone says about setting them up equally. It's just not possible to do.

A 60 lb bow does not shoot the same as a 70 lb bow and will not equal the performance period. The whole reason you buy the 70 lb bow is not to be equal but to gain something.

If you use the same arrow the 70 lb bow is faster.
If you increase arrow weight to have the speed the same the 70 lb bow has more KE and momentum.
There just isn't any equality between the 2 weapons.

example,
Person 1 says that he shoots a 60 lb bow with a 1,000 grain arrow at 200 fps to gain momentum
Person 2 can shoot that same arrow at 210+ fps. Or, he can shoot a 1,100 grain arrow at the same speed as the guy with the 60 lb bow. You gain performance with the higher DW.

Also, the thought that you have to use a heavier arrow for the higher DW and therefore negate the speed increase is just not true.

At 65 lbI shot a 391 gr arrow 282 (chronographed)
At 72 lb I shoot a 431 gr arrow 292 (chronographed)

That's a 10 fps gain with an arrow that weighs 40 grains more.
I've increased speed, KE, & momentum.