There's a couple things worth pointing out about that test.  First, it was on a 440 Mopar.  What works on one engine doesn't necessarily translate to other engines.  Though I will note that the 440 uses the same style oil pump as a SBF (more on that later). 

Second, it we are honest, most of us dead set against HV pumps on engines that don't really need them due to the idea that they waste HP hold that belief because a lot of people we think have a lot more knowledge than we do have written that in books, told us that at the machine shop, etc.  Possibly this is the illusion of knowledge and not actual, empirically tested knowledge, and that's exactly how urban legends get started.

Third, consider that many, many things that get repeated and passed down as proven fact came from peoples' experience with the SBC.  I know some guys get salty about that as Ford guys, but the industry standard for performance almost since it was introduced has been the 350 Chevy.  Where this is interesting is the SBC use a different oil pump design than the SBF (or the 440 Mopar).  Possibly the idea that HV pumps waste power comes from the fact that they do in SBCs (purely conjecture mind you, but where there is difference there is also possibility). 

In summation I also need to point out that this test is extremely narrow in its focus.  It looks only at the effect of various pumps on power.  It did not consider loading on the oil pump drivehsaft/distributor gear/distributor gear roll pin.  It did not consider the effect on oil temperature.  It did not consider the effect on oil aeration.  It did not consider the effect of moving oil to the top end of the engine at the expense of the bottom end.  Even if the test is valid and disproves the power wasting argument there's a lot more to the oiling system than just how much power it uses, and thus a lot more reasons why a HV pump is probably unnecessary and possibly introduces greater risk of failure than a standard volume pump. 

My final thought is that like anything else the oil pump should be matched to the build.  SBFs don't typically have oiling problems.  HV pumps are most effective in engines that have oiling issues, because they need more oil to survive at higher RPM (Pontiacs, AMCs, etc.).  In an typical SBF a HV pump is a solution in search of a nonexistant problem.  Such "solutions" often cause more issues than they resolve.  So, standard bearing clearances, and operating range under 6,500RPM a standard volume pump is going to be just fine.  You go to wider clearances for racing, or if the engine is becoming worn out and your oil pressure is low; a HV pump is probably a good idea.

I think a lot of the SBF "gear and dirveshaft" issues simply come from the myriad of camshaft and gear materials. Folks more often than not mismatch the two.

Speaking of "oiling more around the bearings 'may' increase HP".....
I understood (might be worng!) that mechanical parts glide along on a microscopically thin layer of oil.
IF....and engine has std bearing clearances 'more oil' would not make it float more or slicker-up the surfaces would it? (one of those.......enough is just enough situations)
Am I out in left field on my thoughts?
The increase in HP statement has me scratch'in too!
6s6

My first question would be what the "stock" pump was?  If its was a parts store brand (likely made in China) my supposition would be that the HV and HP pumps were quality American made with the clearances blueprinted, and likely that's why they made more power. 

Now, if it was a quality Melling, etc. then my next suspicion would be that the margin for error on any dyno is more than 1HP, so let's not get carried away thinking "increases" so low are actually measurable and meaningful. 

Most sources will say that 20psi at hot idle is all the oil pressure you need.  If you've got at least that I wouldn't go trying to reinvent the wheel.  Especially if you still have 10psi per 1,000RPM as it revs.  Now, I'll admit 15psi would be a bit concerning to me, and I could see where a HV pump might improve that, because if you think about it: the oil galleries are still the same size.  Try to force more volume through them it stands to reason pressure goes up.  However therein also lies an important point: what we see as pressure is really just a measure of restriction.  If your engine has less restriction you would expect lower pressure (I'm remembering something about your 427 being pretty far off stock). 
 

Wasn’t 10w40 used back in the old days for heavy duty uses?

I took my 68 out for the first time this year, put about 60 miles on it and remembering this post checked my oil pressure.
I thought I had a Melling standard oil pump in it but after watching at the electric Autometer gauge I have my doubts.
I run 10W40 synthetic and at start up It shows 55#, hot idle in drive is just a tad under 50#.
Now I think I may  have a high volume pump, IIRC I did blue print it when I built the 331.