Upright player for hire here....(I play with Rockabilly, Psychobilly, Folk, singer/songwriter, and occasionally bluegrass artists.)
I use a 2x10. 30" wide X 16.5" deep by 13.5" tall. It's shelf ported loaded with Eminence Beta 10 speakers. The Shelf ports are on either end of the cabinet, not along the bottom as is traditional. I did this to keep it short and wide (as the Fender style head the amp is in is very wide.) It's tuned fairly low with those dimensions, and gives a nice sound. I also added a piezo tweeter to get some of the string "clack" when slapping fingerboard for the Rockabilly/Psychobilly stuff. I use either my 200w tube bass amp that I built out of a dead Super Twin or a Trace Elliot Solid State head. (I also use a little 50w Ampeg Bass Rocket for coffee shops and small gigs)
I have a Hartke 4x10 metal cone cab that sounds good... and when building the 2x10 cabinet mentioned above I tried to get the same frequency range...I really didn't use a lot of math, just some trial and error, but I think I got close with this 2x10. I liked that so much that I built a 1x10 that I cut the width to about half. I use it at home with a small 50w solid state head for practice, with great results either upright or Fender Bass.
These may not be the dimensions you're seeking but I thought I'd share my experience. I wanted something that I could dress up like a Vintage American amp to pass on the Rockabilly stage, but with some modern Bass kick. I prefer 10" drivers over 12" models. I think (opinion, not necessarily fact) the 12"s have too much midrange. That is great for guitar but less so for Bass.
I thought about doing a 15" and 10" +tweeter in a single cab instead, but I found the 2x10 to be more than adequate and much more portable in dimension.
j.