As long as you are not afraid to pull a few screws and take a peek inside (and take a couple pix) it may save you a transformer, but then again you may need it for some other things.
BTW the Italian power connector is very different from Europe - three in line contacts (middle is ground) and...
Truth on the tough love part and doubly so on the board swap as there may be more problems beyond, that you may not be prepared for, but the board swap would cure (and would be easier)!
I use the Roland Micro Cube RX even used it jamming in Central Park NY with a bunch of bluegrassers, used it at a Wernick Jam camp in Prague and will use it at a retreat next weekend, but I use it with an Ashbory not a Kala (don't own one, yet).
More watts or more efficient speakers means louder and efficiency generally trumps watts for loud. The two speakers you list are totally different in concept and purpose but the Mackie would get louder (probably twice as loud) and sound better. Mackie lists the peak spl at 126dB and Behringer...
My point is a bit double sided, Gene et.al obviously take the business of music very seriously (I'd love to have his cash-flow), but the stage appearance could be concidered as comical, a hyper-exaggeration of stage personas then followed by all the mock KISS lip-sync 'concerts' in the 70s...
That's what sound guys are - at least the good ones ;-) It is so much easier to leave a channel off than run a new drop on a live stage!
To the OP, Jimmy got it right - as the sweet spot depends on both the mic and the cab, plus live is always close mic'd.
And if it is that far up ask the power co to retap the transformer down 5% or tell them what you find and ask them to check it out, but you may lose power for a couple hours if they need to retap the transformer. There are usually a 5% and a couple 10% taps to correct voltage problems.