Platter upgrade for VPI MkIV?

Slaw, you asked the question about platter upgrades six years ago.  You got several opinions on what to do, in essence, "keep what you have" was the response.  Now six years later you decide, in your opinion, that response was wrong. OK, that's fine.  The problem is when other people seem to contradict it, it's not fine.  Everyone here is expressing opinion, most of us have limited experience, but want to share our experience with others.  That's how we learn.  Sometimes the things we learn don't jibe with our experience, so be it.  Each of us experiences this hobby of ours in different ways, hence the common phrase "your mileage may vary (YMMV)".  In this case you and Stringreen have differing mileage, it's not a big deal.

My $0.02, having been a VPI owner for many years.

Acrylic beats aluminum. Heavy beats light. The type of bearing doesn’t matter; the quality of the bearing does. Each type of bearing has its advantages and disadvantages.

IMNSHO, and that of some experts, the acrylic/lead (which I use) and super platters are the best. I switched my original TNT bearing for the Mark V, which I think is the best (or nearly the best) non-inverted bearing VPI has made. FYI VPI uses a non-inverted bearing as the main bearing in its best belt driven TT, the Avenger Reference with the magnetic platter.

The personal arguments here are of interest to no one.

FYI VPI uses a non-inverted bearing as the main bearing in its best belt driven TT, the Avenger Reference with the magnetic platter.

For clarity, the magnetic drive platter uses a traditional non-inverted oil bath well bearing to support the drive platter which also has an inverted bearing to support and isolate the slave platter. 

Yes, of course.  But the bearing that does most of (indeed, almost all of) the turning is the non-inverted bearing.  My only point was that there is a popular misconception that inverted bearings are inherently superior and non-inverted bearings are inferior.  The excellent performance of the Avenger Reference proves otherwise.   The inverted bearing isolates the slave platter from speed variations of the drive platter, but not from its non-inverted bearing.

As stated, a major advantage of a non-inverted bearing is that it sits in an oil bath.

.....and the major advantage of an inverted bearing is that the majority of the mass is below the bearing / thrust pad's center of gravity. 

I do however, agree with your statement that both inverted and non inverted bearings have advantages and disadvantage and what matters most is the quality of the bearing.

BTW, VPI never made platters with a combination of acrylic / lead or metal, they used Delrin / Acetal.  VPI did for a short period of time made platters out of  both 100%  (frosted) acrylic and carbon infused (Black Knight) 100% acrylic, which by all accounts (including me) were the poorest performing. 

The stainless steel TNT Mk5 bearing with the rulon bushing and heavy stainless steel retaining donut is as good as it gets.  If you have not done already, I would suggest replacing the 0.25" ball bearing with a ceramic silicon nitride (Si3N4) grade 3 ball bearing.  Also, if you have an extra thrust pad, have a local machine shop drill out the tungsten pad and replace it with a thrust pad made from PEEK.