Hi Rod,
Since nobody has commented on your post and I can't go icefishing today, I'll offer some insight from my personal experiences.

It seems like the 5P+ hit my neck of the woods in about the mid-late 80's when getting rid of asbestos was paramount and has since then more or less taken the place of the old "red-rod".
Lincoln still states in their electrode descriptions, 5P is favored where you have heavy painted surfaces to contend with. The reasoning and description are garnered from the somewhat harsh arc-blow (comparitively speaking as you have found out) that helps burn the paint off the base material just ahead of the puddle. This is a true statement but with the advancement of technology in cleaning aids in the last 15-20 years, education, and closer observance to project specifications, welding over paint should no longer be an everyday occurance, even in plant maintenance. In fact the worst of the worst was when you had to weld structural trusswork that had 15 coats of old paint on it and you had to weld into an overhead corner with 5P! You quickly found out what "arc-blow" was all about let me tell you!

When the 5P+ came into our plant I was off welding and hired into the company's Welding Engineering Dept. and participated in testing the electrode for use at our facility. It was my small department of Specialists that recommended our company's purchasing department to buy the 5P+ and phase out the 5P which it did in about 1986.
Previously I had prefered the E6011 over the 5P to run critical root beads whenever I had 100% x-ray (ASME B31.3 read to "severe cycliclic") on small diameter (A106-GrB, 11/2"-2"sch 40 & 80) piping up in the miles of pipe racks. I would check box after box of 5P trying to find a batch that would burn square and wouldn't "toenail" to the side or blister. Seldom could I find one, so I would use E6011 electrodes instead for that work. It seemed pretty tough to find decent 3/32" electrodes back then (60's-early 80's) for some reason! As we found, the 5P+, as did the E6011, always burnt off square with shallower "wagon tracks" then the old 5P using the same joint design. Far and away more user friendly then 5P was the overwhelming consensus in our plant once our welders started using it. Notice that I used the word "overwhelming" and not 'total", it took more then a few years to phase the 5P out (might not be all gone yet?). There were some welders who swore that if you took away their 5P, they couldn't weld.

I have to admit though, there is one type of weld where the old 5P does shine. That's when using it to apply the cap pass to a 2G weld with what we always called the "quick-step" technique. It's a technique that depends upon the cooling rate of the weld puddle and the eye/hand dexterity of the welder. The puddle characteristics of 5P+ doesn't allow the visual aid that's required to do it but the 5P does. I worked with several "golden-hands" that when they walked away from a 2G, it looked like they had wrapped series of the finest braided chain around the joint. You could almost mic the weaves they were that uniform. I admit though, beauty can be only in the eye of the beholder!

Somebody will ALWAYS find a reason to want the 5P (there's an electrode for every use and it can be personal) and that's ok but the 5P+ certainly will continue to overshadow and outdistance it until technology brings on the next generation of electrode to take it's place as it did the 5P.

Please except my apology if my rambling answer/comment has bore anybody.