I have always heard single line systems are good too 7K. Well I would hope so seeing I have personally ran internal 3/8 NPT pickups to 7K.. Not just a one hit wonder either my Old Dakota had a 7 quart pan stock High volume Melling pump and every single pass it would go 6800-7K.
So in theory the Single line should go 7500 or there bouts. and I have also turned the duel line HV stock Melling pump to 8K too.
Im getting ready to address the new race car's oiling system and mock up, make lines etc. And was debating the use of a single line over the duel line external oiling systems.
The single line kit can be pieced together fairly cheap using a static 440 source pickup and utilizing a single line pump cover.
Engine is a pretty serious effort bracket type engine. 499 Low deck fully ported B1 Originals, 14:1 compression billet crank and rods etc.. So it will want some RPM

Bob, my 518 has a stock 3/8 pick up with the OEM Mopar 6 quart 1970-71 Street Hemi/440 6 pak oil pan, I shift it at or above 7000 RPM every run My rod and full groove main bearing clearances are loose(.003+) and I run thin oil, 5W20 WT pure petroleum based Valvoline, non synthetic I do have two motors that have dual line Milidon oil systems on them there both for sale, one is sold actually My next Hi Po motor (above 750 HP) will probally have a external oiling sytem on it due to the cranksahft stroke, 4.5 or 4.375 to avoid the internal oil pick up interferences The current 518 has a 4.300 stroke with BB Chevy 2.200 size rod journals and aftermarket H beam rods, those barely clear the 3/8 pick up, they won't clear a 1/2 inch internal pick up I have seen 8400 RPM on my playback tach twice when drivetrain parts failed in 1st gear No noticeable problems when I tore it down and inspected it

My preference is a single line system with the swinging p/u in a dragster style pan with trap doors ETC. Never lost pressure, or had an oil starvation related failure with this system, but 7550 is max I've been.

Had a dual line system, and suffered from it losing prime if it sat a while. An old timer told me after hearing me complain about it, that I needed to replace or rebuild the pump. He was right, after replacing the pump, it quit doing it, but I've never had that happen with the single line system.

For what it's worth, I use a static dual line pickup, 12 quart DEEP pan, windage tray with scraper built in, A blueprinted Melling pump sandwiched between the Milodon plates. The motor has seen 8000 on a few occasions, normally 7200. Dave

A single pickup system can supply a lot of oil, so if your combo is well thought out I don't see any reason to run an extra pickup line. Another thing to think about is you have two lines between the pan and pump but you still only have the same area of opening in the swinging pickup. So just how much help can the extra line add?
My bet is the only time a dual pickup system helps is when the demand is very high,(too much clearance) or the oil is too cold.
When I was running the no growth radials, my motor was going through the traps at 7800 rpm. No problems. I now go through at 7400 rpm. Thats all I have, is a single line.

My B1 has a single line swinging pickup. When we run it all out I shift at 8300 rpm. Never had an oil issue with this set up. We are over 300 passes with this set up and the bearong looked new at freshen up with 223 passes.

I have single line Milodon systems on both my hemi and my 440. Both turning over 7k rpm.

I have 500 inch setup with a stock 3/8 pickup that I have turned 7000-7500K for two years.

Super Stock Hemi here- single line system, Standard Volume Melling pump, 8 quart system, 8600 rpm shifts.