Upgrade from VPI HW-19 Mark IV turntable

Keep the Mark IV, it's one of the best turntables VPI ever made. I think you would have to spend way above your budget to get better and any of the models you mention would IMHO, be a backward step.
The Mark IV warrants a much better arm. I once had a Mark III and going from a Rega arm to an SME V made a huge difference.
Maybe look for a used Graham 2.2 ..... even a Mk1 Phantom might be had within your budget as would an SME-V. I've seen Basis Vector arms for sale for about $1500 (I bought one!) and at that price you get a real bargain. Basis arms can be a bit tricky to set up on non Basis turntables however.

If you like the overall sound upgrade the arm.

The VPI H-19 MkIV is an excellent high value table. There still exist some additional updates that could further improve your table. 1) Sorbothane suspension 2) SDS motor controller, 3) Platter upgrades. As you have already pointed out, a tonearm upgrade would also yield sonic benefits.

Another option would be to sell the table and purchase a used VPI Classic. You have a good table.

Get rid of that MMT arm. I used that with a MK3 before I upgraded to a SME 309,apples and oranges!

I have the same MkIV table with the Eminent Technology linear track air bearing tonearm that I would recommend on any table. I am content that the table is a great value & you would be better off pursuing a tonearm upgrage rather than starting from scratch. My setup isn't going anywhere. For what it's worth, my best upgrade after this purchase was my ARC PH-5 tube phono stage. The veil has lifted!