Allthumbs,
String companies work out the tension of their gauges to achieve a fairly even balance across all 6 strings; using standard tuning as the base of these calculations.
I use Vestapol tuning a lot, where the 3rd string is tuned up a semi-tone, the 4th and 5th a whole tone. These strings feel much tighter.
I notice this a lot when playing with my fingers.
Customising the gauges evens out the tension with open tunings.
I dont notice any loss of tone, in fact it allows the strings to vibrate more freely, enhancing tone.
Also, my National has a 74 year old cone, and I don't want to crush it, but I like heavy strings.
Using customised gauges helps me achieve the heaviest gauge possible without damaging my neck, or cone, when you consider overall string tension.
In your case Allthumbs, this would not matter as much, as you use dropped D tuning.
I like a little extra tension on the 1st and 2nd strings, as being unwound, the tightness doesn't bother me so much, and the tone is noticeably fatter.
So, you probably have the optimum gauge, execpt maybe you could try a heavier 6th sting, to compensate for the low D.
Might give an extra boom to your bass! (A bit of messing around, I know)
Also, the wrong tension/gauge can mess with intonation on some guitars, but I can't be bothered going into that now.
I also customise the strings on my strat, but as I have to use it for a number of different tunings, and its as solid as a tank, the gauges I use differ from the ones I use on my National.
Also, I have a 1932 spider resonator, that I just use a regular 13 to 56 gauge on, because its bulit like a tank, and I use it for lots of different tunings. (Spanish G or A, open C, C6, standard, and sometimes vestapol).
I play a lot of fretted notes as well when I play
slide, and what I have outlined suits my style of playing. It may not suit everybody's.
This is just the way I do things, only my opinion.
Just trying to help.