Blocked is right that you're overthinking this, but, as far as I know, only one coolant other than OE meets the specs for our car...that's Zerex G-05 I think...but don't quote me.
That said, the most important thing is to change it as per the bottle--I think OE says every 3 years.
Drain completely from engine block drain, rinse with straight distilled by filling up the system with it and driving a bit with heater on...let car cool and drain it. If it's filthy, do it again...then replace crush washer and use OE/distilled mix.
Blocked is right that changing it is more important than what you use...sort of...but there are some issues with gunking if you mix the wrong coolants...and then there are additives that bmw coolant has that are compatible with all the materials in our system. For many here, using OE is just the way to go...and in many ways, avoids many issues.
I'm so depressed. No one wants to come see me in NYC: Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Mangofy your E46!