Owned both for several years, and even ran them side by side in my workshop for a year.
The Fives are still here, in a secondary system. The Sixes were sold to a friend. Both were refinished, new grills and cloth on the Sixes. Both were recapped, with resealed woofer surrounds and new gaskets on all drivers.
They sound different, with the Fives going lower and having a fuller sound, while the Sixes had a punchier sound. Both are quite enjoyable.
I did not really choose to sell one vs the other; my friend just kept pestering me about the Sixes, we are slowly thinning our possessions in preparation for a downsizing of our home, and I have more systems and speakers than I will be able to use after we move to smaller quarters.
So, I let them go. They were fun, and I enjoyed making them look and sound like new again, but no regrets. My tastes have moved to more modern speakers over the past 5 years or so.
If pressed, I would probably say that I preferred the Fives, but not by much. The Sixes do seem to have a slightly cleaner, more linear sound. With some recordings, the Fives can get just a bit congested sounding...but their low end and better power handling make up for this.
Note that if you end up seeking Sixes, the first versions are very difficult to work on, due to the permanently-fixed, basket-less woofer.