That's a really interesting point... I've been engineering my Phantom and she's up to about 66ly while still having the luxuries of a double SRV bay and 32t tank, but it's only going to gain 1 slot (which will add the double luxury of a redundant repair unit).
But relatively, the DBX gains more, and I've never had one yet. Will ponder what I could make with one
My DBX is doing exactly 66Ly now and that is the value ill run it on, but i did set it to use the max size equipment i can fit, if a person runs class 3 instead of 4, and D-rate some stuff it breaks the 70Ly easily (with the GFSDB), i didnt on mine since i preffer losing a little jump range but have speed and maneuvability at the max.
This patch actually brings a all new set of fun to the game in the outfitting department, since we can do alot in all the ships, take the DBX for instance, ill give my example, i got the discovery scanner using up a class 2 slot, that will be freed by the adition of the 2 class 1 slots, but i run a 2G planetary hangar in a class 3 slot, so with the change i can get that to the class 2 slot and be left with a extra free class 3 slot to use... (same goes for my federal corvette, if i ran a discovery scanner on it, its taking up a class 3 slot, wich will be now freed, in mine im not running that since its a total PVE build, but u get my point).
In other ships similar arrangements will occur, wich enables u to do alot.