^The two slot 8540w dual-core maxes out at 8GB.
The four slot 8540w quad-core maxes out at 32GB.
So since he's reporting 16 GB and an i7 chip it must be a quad-core 4-slot model - which could be configured in one of the three following ways to equal 16GB.
The 8GBx2 configuration isn't eligible since he mentions two
memory sticks in the machine he transferred RAM to. So that leaves only the first two RAM configurations.
Looks like he moved two 4GB sticks to the 8570p (which only has two available slots) and left either two
4GB - or one
8GB - stick behind in the 8540w.
That would leave both machines reporting 8 GB - and explain why removing one stick drops total RAM down to 4GB in the 8570p.
That's the easiest explanation that fits the given data.