Suggestions For Analog Upgrade - Tonearm or Phono Stage?

I'm thinking about planning my next upgrade looking for suggestions as to where to get the most improvement for my investment. With champagne taste and a beer budget, I'm definitely interested in used/demo gear.

Current analog setup:
Sota Nova VI table w/vacuum, Eclipse(Condor + Roadrunner) motor controller/tachometer & mag-lev bearing
Audiomods V tonearm with micrometer and silver wiring from clips to RCAs
Nagra BPS battery powered ss phono stage
Dynavector XX2 mk II cartridge

This feeds into:
BAT VK51SE linestage
Krell FBP-300 power amp
Soundlab A3 electrostatic speakers

I've been pretty happy with the Nagra and certainly appreciate their battery-powered implementation that gives me the advantage of being off the noisy power grid, while not suffering the limited dynamics that much battery gear has. But I've always been romanced by a quality tube phono stage. RFI interference in my former locations always led me back to SS phono to eliminate the noisy headache. Now I'm located where that may not be an issue.

One the tonearm side of things, I do have an option to seek an Audiomods upgrade to Series VI, which replaces the aluminum drilled armtube with a new carbon armtube. It also adds a new anti-skate methodology reportedly more stable and user friendly than the older style "fishing line & weight". This route would be low cost, but entail cross-continental shipping and the associated wait times. 

Any plan to replace either piece would be funded from sale proceeds plus a modest incremental investment. That translates to phono stages selling for used at $3K-$4K or tonearms selling used at ~$2K-$3K. Which component would you expect to make the bigger improvement in this system and what specific models that you've heard would you recommend? Cheers,

Spencer