Partial update.
Got both basses back yesterday afternoon and took one to rehearsal last night. Westone Thunder 1A dropped a semi-tone. Compared to the Tomastik flats on my Fender Jaguar, which I had been using previously, the D'Addario chromes were MUCH better. The extra guage and obvious tension in the strings made playing feel more natural. We also drop down the E to D for 'Slither', so I effectively dropped down to C# - handled it nicely.
I can still make no comparison with same strings played with regular tuning but as it was last night was a big improvement.
Have to add I am loving the Thunder 1A bass, too. Exactly the right sound I have been chasing when used active but rolled back a quarter turn. And it is a joy to play.