I did get rid of it (the M66) a long time ago.
That extra 200 FPS makes a world of difference
I believe I went to great lengths above to point out that "that extra 200 fps" may or may not be there.
Even if it is there,,,,I highly doubt it makes any difference at all @ SD ranges, which are measured in feet not yards.
Stretch that range out to yards & - yes - velocity becomes more important.
This is absolutely nothing more than good old common sense...
Main stream ammunition manufactures have been putting out a "one size fits all" product for decades.
The same 125 gr load that goes into a 1 7/8" snubbie fits into an 8 3/8" Long Tom & everything in between.
Using the old rule of thumb of 50 fps loss for every 1" shorter barrel.....just the difference in barrel length alone makes a difference of what?
Throw in ES of shot to shot variance and things get even wilder in that respect.
What that tells me is the ammo makers know there's going to be broad performance band (velocity spread) and they make allowance for it.
While optimal bullet performance may be tuned for one barrel length, perfectly acceptable performance is possible on either side of optimal - well up to a couple hundred fps.
If 50 or 100 or even 200 fps gets you all worked up, then be my guest...knock yourself out and spend you hard earned money chasing it.
I honestly don't care about a couple hundred fps.
Three hundred? Yes. That's where I begin to take a more critical look....but...there again it's all relative.
BTW - if you still feel that 100 or 200 fps is "critical" consider this.
Speer uses the same 125 grain bullet for the .38spl +P that's used for the .357 mag....
Speer only catalogs one GDHP in 125 grain for the .38/.357 mag.
(They do however catalog a different product number for the "short barrel" 125 grain..HOWEVER - the finished "short barrel" ammunition is a different product)
The .38spl +P out of the 4" test barrel is 950 fps.
The same bullet out of a 4" test barrel in .357 mag is 1450 fps.
That's a whopping 500 fps difference.
Yet - despite such a huge difference, time after time after time after time - people have done "back yard" expansion tests of both loads and report good to excellent results.
What that tells me is the the spectrum of performance is much, much wider than anybody cares to admit...