If you are playing with a band, in all likelihood you ARE going to need to play a proper two handed piano part on at least a FEW tunes... Yes, you CAN get away with a 61, but it's a huge compromise for piano playing. 76 has been my preferred type of key-bed for decades. Big enough for the majority of piano parts, a fraction of the weight of an 88, and still usable for organ parts, which a wooden 88, IMO, is not...
Also, take into consideration that as a band keyboardist, you will also be likely to need splits (piano lower, brass upper, pad lower, synth solo upper, etc.) and a 61 gives you a lot less to work with there. Unless you want to haul around a stack of 61's, a single 76 gives you the best opportunity to cover all the bases with the minimum of gear. The true arranger player, usually simply using a small area in the lower to trigger the accompaniment, doesn't have the same need for the LH area to be significant. But if you are band playing, it's a LOT more important.
I would go with the 76 every time...
_________________________
An arranger is just a tool. What matters is what you build with it..!