Re: MDS Question
The same 4 cyl's get deactivated each time.
What happens is that when MDS activates, is an initial Air-Fuel charge is injected, it is ignited, but the exhaust ports don't open. This charge is left in the cylinder and acts as a spring as it is constantly being compressed and then assists in pushing the deactivated cyl down on it's normal power stroke. This is also said to help keep heat in the cyl while it is deactive.
This 'Spring' effect also helps the engine run smoother when it is in 4cyl mode, since it helps even out dead spots in the power strokes.
When MDS disables, the Exhaust port opens releasing the kept exhaust charge, and then the intake vales open giving the cylinder a fresh air/fuel charge and it moves on it's way.
As far as wear across the Cyls. It's hard to say. You might see less fouling on the spark plugs over time, or possibly less deposits on the cyls. But, it'll be minimum since the engine is not in a 'Stress' situation when MDS fires. It only runs in absolute optimal situations -- ie, when there is little to no stress on the rings and pistons.
MDS is a brilliant technology. It was very well developed and thought out. I recommend Spending some time on the Google if you want to learn more.