I've had my homemade oil catch can in place for approximately 6,650 miles and wanted to present my results. I have used Mobil 1 0W-20 the entire time without an oil change and have witnessed a drop in oil level equivalent to about 1-2milimeters on the oil dip stick. I see lots of highway driving at or above 4K rpm.
The total oil consumption and amount of captured blowby seems reasonable and I am not concerned. I will however keep my catch can in place just to keep the intake and top end nice and clean.
I collected about 47ml (1.25 oz) of oil.
Here is my set up. I am using a slightly modified water/air separator typically used in air pumps and I have it attached to the windshield wiper fluid reservoir.
Once I get to 15K miles on the same oil I will do a blackstone UOA and present those results as well.
EDIT - I am using Mobil 1 0w-20 Extended Performance.