Yes Pressure and volume are different but they have each a great effect on the librication system,
Chevrolet Racing further discovered that no more than 45 psi of oil pressure was ever needed for any reason. Bear in mind two things as we ramble down this side road: First these are 600+ HP (sometimes way +) small block V8's, not stock engines, and second, they're predominantly plain bearing engines. The YZ450 is predominantly rolling element bearings that can live with no oil pressure whatsoever (and indeed, cannot contain any pressure) as long as they get a supply of oil. In fact, the main bearings in the YZF have no direct oil feed delivered to them at all, just incidental oil from drainage. The only place in the engine that are pressure fed is the camshafts. The rod bearing is directly fed, but it's a metered amount, and there isn't any pressure in the part of the circuit between the nose of the right crank axle and the con rod because, as I have said, the bearing won't hold any.
The other factor that remains is that oil pressure as nothing whatever to do with the lubrication of the rod small end, since everyone's small end bearings are lubed by indirect means like oil thrown off by the big end. In engines with floating, rather than pressed in wrist pins like the YZF and most other bikes, most of the actual movement between parts takes place between the pin and the bores in the piston, and very little in the rod small end. IF there is in fact a defect with the '14 rod small end, it will be one of these:
- The clearance is excessive, allowing the wrist pin to "rattle loose" over time because of a manufacturing error
- The clearance is excessive, allowing the wrist pin to "rattle loose" over time because of an incorrect specification by the engineers
- The materials used in the rod and wrist pin are incompatible to the task at hand
- The design of the rod small end is such that is interferes with oil entry
- The design of the rod is simply too weak
If the condition is such that one needs to choose or avoid a certain oil over others when all of the oils considered meet the manufacturer's requirements, it's not the fault of the oil.