Does plated steel shot pattern better?

It's funny, given my propensity to agonize over shotshell minutia, but I've never given plated shot much thought.  I've purchased it in the past, but only because it was what was available at the time.  Even when I was at my most vulnerable to suppliers' marketing, the alleged advantages of plated shot just didn't seem to gain any traction with me.  First claim is rust resistance.  To that I counter that, 1) I've never noticed the plated steel heads of hulls being particularly rust resistant (albeit, they may have a different plating), and 2) who cares?  Second claim is it patterns better and penetrates deeper due to the "slickness" of the plating.  This just sounds like flim-flam.  

But last week, someone asked if anyone had done a side by side comparison of the two, and I realized that, though I'm sure it has been done before, I've never seen or heard about it.    

I happen to have some zinc plated #BBB from Precision Reloading as well as some unplated #BBB from Reloading Specialties.  Ten pellet averages are 7.29 grains each for the plated and 7.4 grains for the unplated.   

 So loaded up some goose loads.  

12 ga 3" Fed. .090" base one-piece (or IBW, or whatever BPI calls it)
Win. 209
46 g Lil'Gun
MultiMetal 2.75"
1.375 oz #BBB steel (=83 pellets plated; 82 pellets unplated)

This is a down loaded version of a +P load I had tested at PRI and posted here.  The original load was over SAAMI pressure for a 3" chamber, but under for a 3.5", and I assume loading down 2 grains and switching to what I assume is a cooler primer will lower PSI somewhat.  Whether or not you think my assumptions are well-founded enough to follow is up to you (remember, this is the internet). 

I don't know how I'd test penetration in a meaningful way, but I can make holes in paper!

Remington 870 Express Supermag with a Patternmaster Blackcloud Full choke at 50 yards:

Here are three patterns with unplated shot.

46/82 = 56.1%

51/82 = 62.2%

47/82 = 57.3%

And here are three patterns with plated shot

43/83 = 51.8%

52/83 = 62.7%

54/83 = 65.1%

Here we also get to see the exciting effects of recoil after five goose loads at the pattern board.

That's only three shots each you might say--not the industry standard.  Yes, but as I stated before, I'm more interested in comfort than rigour when it comes to science, and six boom-pows was enough for my shoulder.  Also, it was really hot.  

But be that as it may, I still think there's enough to shed some light. 

Unplated averages 48/82 = 58.5%

Plated averages 49.7/83 = 59.8%  

Even if I round the plated up to the less annoying 50, it still only comes out to 60.2%.  Still not a very compelling difference.  And the pellet distribution seems pretty comparable.  

So I'm willing to say plating makes no difference to steel shot patterns.  (...at least, to 1.375 oz of #BBB's.)