Let's not drift off too far with this post, why not just help the person who started it with his engine oil question and other fluids.
Indeed.
It doesn't tell you an awful lot just going by the label category for viscosity, you really need to check the tech spec from the oil manufacturer. Nominal viscosity bands cover a relatively wide true range, and some manufacturers tend to make oils at one end of the range (Castrol bike oils tend to be at the low end, so the 10W40 is only just thicker than the top end of the 10W30 band for example).
Use what the manual recommends and you won't go far wrong.
0W-30 and 5W-30 will have very similar viscosities at 20C and upwards to the normal operating temp. What is usually more important is the quality of the additive pack, just go with a well known brand, Castrol, Mobil etc.
Bearing protection is about more than just gallery pressure, it is as much about flow rate as anything. Wear of valve train components is about additives. Bore/ring wear is about temperature stability. Longevity is about breakdown rate and ability to cope with contaminants (TBN etc).
FWIW when I come to do my mk.3 I intend to use the Honda 0W-20 stuff, it's not going to be junk.
https://www.coxmotorparts.co.uk/