Rega RB300 Best Upgrade & Vertical Tracking?

I would go with the RB300. The Audioquest PT6 that I had mounted on a HW-19 always felt cheap to the touch and eyes. I can't say anything when comparing the sound between the two, but the RB300 has a good history among many who use it.

I have an RB300 on an HW19 IV and I find it to be excellent. I also use a VPI VTA adjuster which I wouldn't want to be without. I certainly don't change VTA for each record, but in setting up a cart I find it essential to get the arm level and then find the best spot for standard thickness records going by ear.

Dear Onetwothreego: Yea, that's the way I am considering to go... in the direction of your set-up. Do you have the Super Armboard on your table? Will I be able to get enough vertical clearance with the 20lb TNT platter and Super Armboard by using VPIs VTA adjuster, or will I still needs shims? The two cartridges that I have in the meantime are the Grado Platinum Reference and the AT440mla. I am also trying to figure out all of the issues regarding rewiring.

With a Super Armboard you will have no problem with the TNT platter. I don't have the Super Armboard and mine is a shade low so I have added a layer of acrylic under my regular armboard. With the my early model VPI VTA adjuster, I have lots of room both below and above armboard level, since the arm can move in quite a range.

You should contact VPI and talk to them about exactly what you want to do for full assurance that things will level out properly.

I used a Discovery Plus4 phono cable with my TT for a few years. I really liked it. It is extremely musical. It's main emphasis is mid range and has a great HF charecter. The RB300 wire upgrade from Discovery uses Plus4. HiFi+ did a great review of the Discovery-vs-Incognito wire. They choose the Discovery Plus4.
Having said that I can say that now using the Discovery Essence phono cable has shown some of the areas lacking in the Plus 4, namely bass. It does not go as deep as the Essence or have the overall bass impact. The Essence HF also exceeds the Plus 4's a bit. BUT, the Plus 4 has a magic that the Essence can't touch. The Essence can't be put into the RB300 so that is not an issue.
Now I recently put together a 2nd sys and have a RB300 with the Michell weights and the Incognito wiring. I have yet to set it up so I can't really say how it might compare.
Some people really think the PT6 may be better than the Rega. I asked just this same question here and on the "VA" site. I think if I was in your shoes I would upgrade my cart. and save for a better arm than the RB300, say a 10" VPI or SME or a OriginLive.
I'd go for a Pete Riggle VTAF over the VPI unit. VPI made two different units for VTA. I have read some +/- about them both. I will probably pick up a Peter Riggle VTAF soon.
He makes a nice heavy weight as well.