Seriously!

But (seriously) I've had that happen on several occasions, and I don't know if I would have been able to stay upright if I'd been sliding at different speeds front/back.

The Attack/Force are probably the same rubber compound, which makes the coefficient of friction likely to be pretty much the same, even with slightly different diameters.

If you're changing 1) diameter, 2) tread pattern AND 3) tire compound, it's more likely that you're going to get differential grab.