I agree with the other posters - I would stick with the 0W-30.
But, if I were to mix, I would go with the same manufacturer. This is the easy way to do it, but it's wrong! Read on ...
1 litre of 0W-16 mixed with 1 litre of 0W-30 would yield 2 litres of 0W-23
2 litres of 0W-16 mixed with 1 litre of 0W-30 would yield 3 litres of 0W-21.3
3 litres of 0W-16 mixed with 1 litre of 0W-30 would yield 4 litres of 0W-19.5
5 litres of 0W-16 mixed with 2 litres of 0W-30 would yield 7 litres of 0W-20
... and so on. This is not a reliable way to calculate viscosity.
Given that there's a range of viscosity for any given weight of oil, it really all depends on the manufacturer. The alleged 0W-23 (the result of a 50/50 mix) might have a viscosity that falls into the 0W-20 range. Ditto for all of the others. Let's check: https://www.oilspecifications.org/articles/introducing-the-sae-8-and-sae-12-viscosity-grades.phphttp://infomechanical.blogspot.com/2010/09/lubrication-oil-meaning-number-sea-20w.html https://www.bobistheoilguy.com/viscosity-charts/
SAE 16 weight has a range of 6.1 - 8.2 cSt @ 100 C.
SAE 20 weight has a range of 5.6 - 9.3 cSt @ 100 C.
SAE 30 weight has a range of 9.3 - 12.5 cSt @ 100 C.
The overlap between SAE 16 and 20 is weird; I wonder whether they'll up the lower range of the SAE 20. As is, an oil with a viscosity anywhere from 6.1 to 8.2 could be either a 16 or 20 weight. This confusing article seems to imply that the viscosity range for SAE 20 will be raised from 5.6 to 6.9 cSt @ 100 C:https://www.oilspecifications.org/articles/sae-16-viscosity-grade.php
Mobil 1's 0W-16 has a viscosity (@ 100 C) of 7.2 cSt.
Mobil 1's 0W-20 has a viscosity (@ 100 C) of 8.8 cSt.
Mobil 1's 0W-30 has a viscosity (@ 100 C) of 10.9 cSt.
If you were to mix Mobil 0W-16 and 0W-30 50:50, you'd get a viscosity of 9.05, still near the top of the SAE 20 viscosity range. If I were to mix, this is what I'd do. But, let's say you have a 5 litre sump - one bottle of M1 0w-30 and four of M1 0W-20 would give you a viscosity of 9.22, near the top of, but within, the SAE 20 range. No SAE 16-weight required!
Good question, I learned a lot going down this rabbit hole.