I would say you need at least 6 inches based on my Comet VI -
Just measured my Comet VI - it is 6 5/8 inches to the highest point of my tonearm - but I have a Audiomods Series VI tonearm on my Comet VI (Sota did a custom order for me) and I have the brass feet pucks under the brass spiked feet, which adds a little - I would estimate the brass pucks under the feet add 1/4 inch;
I expect the standard Rega tonearm would make it a tad shorter; the 6 1/4 inch number from Sota is likely accurate for the standard configuration without the feet pucks, but the tonearm counter weight would be the highest point and I suspect is a close fit with the dustcover - which is why I would say you need at least 6 inches. If you change the brass feet (they add 1.5 inches ) to a shorter set, you could likely knock off up to another inch (you still need some feet - the bearing well protrudes approximately 1/2" below the plinth).
I too have not had a better table than this. Build quality is outstanding, solid speed and very quiet. Sounds fantastic. I was actually searching for a table to fit the tonearm, and the Audiomods tonearm is Rega geometry. The worry was that the tonearm would not fit under the dustcover (the VTA adjuster is a little taller than the rest of the arm) but it does and the table and tonearm with the dust cover look like the were designed with each other in mind. I will add that I have a Falcon PSU for speed control (easy add on for this table - just plug it in).
Hope this helps..; if you need more help PM me and I will see how short I can make mine and let you know.