About 12 years ago, I bought the VPI HW-19 Mk2, and then upgraded to the Mk3, and finally the Mk4 version (with a Rega RB900 arm and Grado Reference cartridge). I had a chance recently to do some extensive listening to the Scout with the JMW 9 arm. Based on my personal experiences, I would recommend either the Scout/JMW9 arm (first choice), or upgrading all the way to the HW-19 Mk4 version (which has been consistently acknowledged as one of the best high-end turntables at its price). I would not bother to upgrade to the Mk3 version.
The HW-19 Mk4 table is good enough that it will benefit from a very good tonearm and cartridge, so if you decide to go for this ugrade, you should be prepared to get a high quality tonearm and cartridge at some point if you expect to get the full performance that this table is capable of.