I can't compare the BX to the JD because I've never used that JD. I can tell you that my BX 2230 (last year's version of the 2350) cuts a lot faster than my JD L130, but that's because I have a 60" mower now, instead of a 48". Besides, the diesel engine and heavier transmission on the BX allow me to mow up my hills at a much more consistent speed. Finally, the suspended self-balancing mower deck on the BX makes a more even cut than the JD's rigid deck.
As far as gas use, I am AMAZED at the fuel economy of my BX. I can't actually tell you how many gallons its taken to put 50 hours on my BX, but I can tell you its less than half what my JD used (which was a much lighter tractor, with a 23 HP Gas engine).