I think the BX-23 could handle the job, but there are a couple of things you need to keep in mind:
(I am a huge BX-23 fan, so don't take this as criticism, just an effort to be factual. /forums/images/graemlins/grin.gif )
As always, you need to be mindful of the size of the machine. The BH does not have a long reach, so even a shallow trenching job requires that you move the tractor frequently. At five feet of depth, you will be moving a lot.
Of course, that will be offset by the fact that you will be sitting in one place for a while in order to achieve the desired depth. That little bucket doesn't move a lot of dirt in a single scoop.
The limited reach means that your spoils pile will be close, and may need to be moved out of the way occasionally, taking time from the actual digging.
I've come to regard myself as a pretty fair BH operator /forums/images/graemlins/shocked.gif -- but that's probably because the BX-23 BH is so well designed that it's easy to operate. However, since I'm an occasional user and not a professional BH operator, I find that after an hour or so I start to lose my coordination and need to take a little mental break to get back on track.
I love the sound of that little engine, but having that thing screaming behind you for hours at a time (you need to run at 75-100% to get the needed hydraulic power) can really contribute to mental fatigue and the need for occasional breaks.
So -- bottom line -- know what to expect, and keep reasonable expectations and you will be able to do the job and will be happy with the BX-23. Realize that a big job will take a while to complete and enjoy youself while you're doing it (it's FUN!). And smile knowing that you're only burning about a half gallon of fuel per hour, and that if you had to do this by hand with a shovel, you wouldn't even be able to get out of bed the next morning!
/forums/images/graemlins/cool.gif