It’s common to have 5-10% differences on benchmarks between Linux and Windows on the same hardware. iPadOS is even more different (for example, no swap, and many other similar fundamental optimizations for single-app usage).
You can't benchmark a chip. It all depends on how much power and heat dissipation the actual device can provide. When the MacBook Pro comes out it should run circles round the iPad. And there are no Snapdragon X devices yet
Sure you can. Measure performance when not thermally throttled and at the lowest speed / no boost. All real devices will fall in between those numbers.
