That’s actually a very good point and something I briefly thought about doing.
Different string types make a huge difference in the sound of any given bass. I actually considered (for a very short time) buying six sets of a middle of the road plain Jane string (D’Addario XL nickel rounds come to mind). But figured I’d likely have to go thru a full set up on some of the basses, adjusting relief and action and intonation, etc. Big PITA.
With the exception of the BlingBird, I’ve played these basses enough that I kinda know each if their strengths and shortcomings and can pretty well predict how they’ll respond to different strings.
At this point I think it would be safe to assume that if all the basses had XL nickel rounds the Greco would still hold top dog position, the next two (Goth and BlingBird) could possibly flip positions (EBCF really bring the Goth to life, take those away and it would most likely drop in rank). The 2015 was born to have tapes on it, take those away and it definitely drops. The bottom two (2013, VP) could flip, the VP is very string sensitive and sounded phenomenal with EBCF but horrible with DR Silver Stars, the Fender strings are the best rounds I’ve found for that bass.
On the other hand, equip each bass with EBCF strings and the Greco would still dominate, the VP might jump up just below or tied with the Goth and possibly bump the Bling to fourth place. The 2015 would suffer immensely and possibly fall to last.
So it’s not just a matter of all the basses having the same string, it’s also a function of which string that is. Of the bunch, the one bass that seems to shine bright regardless if string selection is the Greco. I haven’t found a string yet that doesn’t sound perfect on that bass.
Another test I was seriously considering would have been soundly discounted in most TB discussions but actually makes a lot of sense to me. Basically I would take a bass and run it thru all three heats adjusting pup volumes and tone pots until I found the magic setting that sounded best overall for that bass. Then do that with each of the other basses. Once they’re all set to their best setting compare them all back to back. I’d expect the ranking to be much much harder with a lot of ties. I might still do this once I get the sound file posting figured out.