Jean, thanks for replying re the consistency question (I'm catching this thread occasionally between visits to the orthopaedic surgeons).
My testing concurs, high heat or freezing cold has very little effect on Hitachi injectors as used on a Datsun Z car or the higher capacity after market equivalent when driven from the P&H boards.
I wouldn't expect this to change much with other injectors provided they are in the impedance range the P&H driver boards are designed for.
This is not the case with OEM Datsun injectors and resistors where the injectors run extremely hot in high heat testing.
As always, the environment in which they are used is a significant factor and in my case that is summer shade temperatures of 43 degrees Celsius, engine bay temp often 60 degrees higher. Winter is the opposite, sub zero mornings being common.
Re the question whether OEM's used lo-Z because they were cheaper, no that wasn't the case.
Initially, there wasn't a choice between hi-Z and lo-Z injectors, all were lo-Z. Improved manufacturing methods made the hi-Z feasible and reliable (the wire gauge used in in hi-Z injectors is remarkably thin).
If there is a choice between the two, hi-Z may be the better option but that's not always possible without undesirable modifications to an existing engine.
Again, for an OEM this is a cost cutting exercise - no resistors means less components and zero failure rate from them. The devices to drive the injectors are cheaper too
Datsun 260z 2/2 with 280z/MS3+/5spd for the road
Datsun 240z with 280z - broken
Nissan E24 Urvan with 260z/Megajolt/5spd parts hauler