For some reason, I went through my old Judy Collins Songbook. It first came out in 1969 and is still in print (I believe). So it has staying power, even though it would not appeal to everyone. Her early career was guitar with bass backup, later, the piano was used. The Songbook has 55 songs, all of which can be played as written with 76 keys. 29 songs can be played as written with 61 keys, and another 19 can be played with a 1-octave up transposition. This leaves 7 songs that would require 76 keys, unless you transpose to a new key. For me, a 76-key board is worth it for that last 12%. Your songbook may differ.

People use autoaccompaniment in different modes. Scott uses full keyboard mode so 61 keys should suffice. People who use 1-finger mode or a standard fingered mode will in general find 61 keys enough. I happen to prefer what is called Fingered 2 on the PSR8000 and I think On-Bass fingered elsewhere. In this mode, different inversions sound differently. While the default split for autoaccompaniment is about 1.5 octaves, this mode really calls for at least two octaves. For example, a B7 chord with B bass cannot be formed on the bottom 1.5 octaves of the 61-key board. This leaves only three octaves for the right hand part. Depending on the key, this can seem like only two octaves. With a 76-key board, you can get two octaves of autoaccompaniment plus more that four octaves on the right hand side of the split.

Having a 76-key board requires external speakers, whereas 61-key boards typically have speakers (and amplification) built in. Even where external speakers are used, the internal speakers can be helpful as monitors. In my mind, the most important tradeoff between 76 and 61 keys is the presence or absence of internal speakers.

JCKeys asked about the GEM SK760. This is electronically the same as the SK880, which has 88 keys. We have an active member who uses this keyboard and you should get his opinion. My problem with this keyboard is that it does not store many custom styles in solid-state memory. If you want to play around with the thousands of free styles available on the web, better style handling would be desirable. Also, the sound ROM comes up short--under 20MB, while the soon to be introduced PSR9000PRO is at 48MB. It might be worth waiting for the next generation GEM arranger. I do think the ability to read samples (especially multisamples) in commercially available formats, mainly Akai, is a big advantage of the GEM.