ime this is little to do with the width. The sidewall reduction using a 150/70 gives the same axle drop (hence rake/trail change). And this makes a huge difference to handling esp with an E-Max on the rear.
I have a theory (though it will not be cheap to test - involving custom rims) that massive width differences front to rear affect handling more than one might think. It's all to do with crown radii.
It does, it does. The contact point on the wider rear moves toward the corner's radius center point more than the contact point on the front wheel moves as the bike angle relative to the road increases. Thus a line from front contact patch to rear contact patch changes angles as the inclination angle increases with the effect of reducing the effective turning radius. So the more you lean the more you have to steer.
Then there is the effect of the change in the center of gravity relative to the contact patch centerline which the shift in contact patch line inward moves the CG outward creating a moment that wants to stand the bike back up. The net effect is it takes more and more rider input the greater the lean angle. This effect can easily be felt at slower speeds on crowned streets or near a curb even traveling straight ahead.
On the plus side, the old girl stands right up when exiting a curve which makes her feel more svelte than she actually is. I suspect the Touring models are easier to ride fast then the standards.