Without considering the brand..I think there is a common difference in the player...not the number of keys itself..

If you are "only" an arranger player (and some easy fingering at that)..with a melody line or counter melody line..then yes 61 keys is even overkill (49 could work).. ).

But if you make "full" use of a keyboard that just happens to be an arranger (absolutely the best type of keyboard)..76 keys is a must..period..

Playing left hand chords in more than a root inversion, or playing left hand bass , with enough right hand range to "play" chords and lines without range restriction..(and turn the arranger , auto stuff off, once in a while)..
Using the great features of multi zone across the board (3 or more)..not enough room on a 61...

I know you guys have heard this before...and the guys (mostly) that are saying 61 is more than enough..are the strictly arranger players...missing out on the full potential of even the mid line boards...

We haven't even mentioned playing Piano and EP (again 76 a must)....oops ..maybe I did just mention it..

I do play both a 61 key arranger with the band...and a 76 arranger for my solo/duo work.....It is like night and day..76 rules over 61..

I had the same feeling when I used evenly matched boards like the E50 and E-60...76 keys just allow you to do much more in a natural playing manner..

The difference comes down to the player...