First, I salute you for switching to Mobil 1, I swear by Mobil 1 (For anybody reading this, I am not going to get into a debate about motor oils) and have used it exclusively since 1988, it gained me a consistent
1/10 second in the 1320' when I first used it in my 72 Duster in 88, it was used in my Daytona in 1990 starting with the first oil change.
I still only change my oil/filter once a year, however, I only drive about 3000 miles a year.
The only thing I can tell you about switching to Mobil 1 and this is not a bad thing...
It will over time clean all of the varnish that has accumulated on the engine parts and it will clean any sludge that has built up from using dino oil, this will not happen overnight, it happens over time with continued use so when you see the oil turn black quickly it is not a problem, it is doing its job and still protecting with quality
Mobil says that the oil being "slipperier" and leaking past oil rings and seals is a Myth
Since you are switching to a synthetic on an older vehicle I would recommend using Mobil 1 "High Mileage
which I switched to about a two years ago.
As far as why you are burning oil, yes a restricted/open PCV system may/can cause blowby issues.
Other causes of burning oil would be valve seals, valve guides, worn oil rings or turbo seal issues.
1)The issues with the PCV systems on our cars is the PCV hose gets soft and collapses or the grommet on the valve cover gets hard and cracks.
2)Are the spark plugs showing any signs of fouling?
(There are two types of oil fouling, the wet oil on the plug that we are all familiar with and an "Ash" fouling.
3)Is there any oil in the air filter housing.
4)Is there any oil in the charge piping from the turbo to TB?
5)Is there any smoke coming from the oil cap opening with the cap removed and the engine running.