Hammer,

I gigged with the SD1, SD1+, SD5, and the Midjay.

I'll have to say if it wasn't for the 16 registration tabs on the SD5, I would say the SD1+ was my favorite keyboard.

It covered every genre of music, all of sounds where great except for the acoustic guitars. Registration call-up was a slight hassle but worked.
I never loaded any additional sounds, or added additional styles. The vocalizer and effects are good, imho better than yamahas.

I do like have the speakers on the SD5 for monitoring if needed. Riff feature is a personal take it or leave it.

I do find I look for a few styles with the SD5 that I think are missing.

I love the Midjay series, the reg midjay has about 100+ of the SD1 styles , and the midjay plus has about 140+ of the SD5 styles.

It can be played using another keyboard, can play wav and mp3 files, it can use long character naming of files.

Any of the Ketrons that you pick have that sound and you will be very pleased once you get familiar with the operating system.