I can't speak as a giggin musican, but I have a 61-key arrangers and a 76-key controller, and I vastly prefer the 76 keys. I have gone through my music books and found a good many songs that were not arranged for 61 keys, but fit easily within 76 keys. When you split a keyboard, 76 keys allow bigger sections. In addition to the controller and the arranger, I have an XV-5080 sound module which can load samples. Sometimes the soundsets are cut off when the 61 keys are used, but rarely when a 76-key board is used.

A major factor in a decision on the number of keys is whether or not you want internal speakers. If you do, then 61 keys is more practical. If you do not, then 76 keys gives more playability for the same weight.