I will step into this - but very carefully. With waders. And stay very close to the shore....
Any time you are generating work - be it flow or pressure - you are using power in order for it to happen. The builder for a pretty well known Super Stock car once confided to me that a standard volume pump was worth 9 horsepower over a high volume one. I cannot recall ever running a back to back comparison on that, but it feels on the close/high side of "right".
On my personal engines I run a standard volume oil pump. On most customer engines I run high volume pumps. Much of that is due to perception. I can absorb any risk from "low" oil pressure, but my customers like to see a larger number on the gauge. It's one of the few things that an average person can see that provides a window into the function and health of the engine, and the general feeling is "bigger is better". Most of them would cringe if they saw 52 pounds at 700 HP and 7000 RPM, yet my personal engines live there all the time. Not only can I re-use bearings in my EMC engines - I do. Often.
I consider oil pressure to be a "gotta have some" kind of value and not a true indicator of durability potential. The pressure we are reading on the gauge is the supply side, the pressure supporting the critical rod and main bearings under 1500-2000 psi loads is largely generated by the bearings themselves as they rotate. Provide the bearing enough oil to offset clearance leakage losses and provide cooling and let the bearing designer take it from there.
The rocker tins are extra drainbacks - directing oil leaking from the rockers into the valley. Takes a lot of the flow away from the end drains. Unfortunately they don't work well on many aftermarket rocker systems. Remember that the original engine was designed around crappy, filthy oil at really low RPM for a very long time. We live in a different world with our builds now, and really do not need that much flow or drain area anymore. Use them when you can, but don't feel bad when you can't.
Volume is rotation of a given pump cavity moving a given fluid at a given RPM working against a given orifice. A change to any of those "givens" will change the system. Pressure reflects the area of the orifice as a restriction to flow, and will rise with RPM. Any time you change the size of the orifice, the pressure will drop. The orifice in an engine is the total of all the clearances in the complete package, some are not as obvious as it may seem. Rods, mains, cam, lifter to lifter bore, rocker to shaft, valve lash all have an effect. One of the clues in identification of a valve float condition on dyno is to watch oil pressure - it will fluctuate if you lose valvetrain control as the parts uncouple.
If you are doing things - or tolerating things - that increase flow through the system, a high volume pump will mask the condition and help put a better number on the gauge. It may mean absolutely nothing to the function, but it does certainly feel nice to see 20 or 25 pounds at idle on a hot day...my personal engine might scare you...
I went away from the 20W-50 a long time ago after seeing a modest, but real power gain from running lighter oils. In the contest stuff we are running 5W-20, but I still have not fully wrapped my head around using that every day - and I use 10W-30 most of the time. Like the standard volume pump - the gains are single digit. But find 5 horsepower in 10 places and you're doing pretty darn good.
I have not seen any power on the dyno with a windage tray - I have tried that one. But its still likely valuable in a car with acceleration dynamics, and I use them often. I have definitely and repeatedly found power in getting the crankshaft up and away from sump oil. Every time we have made the pan volume larger and deeper we have gained incremental power. The best pan on a dyno is probably a bathtub or a 55 gallon drum.
Valve springs do make their own heat in operation. But its pretty modest in the environment most FE engines run in. Spring oilers are important in Cup motors that run 10,000 RPM for four hours, but not a real benefit for something at 6500 RPM for 10 seconds. We have enough spray and mist in the covers to keep our springs pretty comfortable - remember that Cup level stuff is also vacuuming every possible bit of pressure (and oil mist) out of the crankcase with the dry sump. A very different environment. Sometimes we need to separate the visible problems caused by supply issues - bad parts, tolerance stacking, debris - from the system design issues or opportunities..
