If you need to do splits or LH bass, and need to stick with a 61, some 61s are more suited to this than others. One feature that helps is the ability to easily switch the octave on just one side of the split, on the fly. So for example, if you find you need to get to some keys out of range with your right hand sound, you could quickly shift the octave of that sound without also switching the octave of your LH sound. Another feature that is useful is some way of changing the sound on just one side of the split, without creating a glitch in the sound you're simultaneously playing on the other side of the split. Some boards let you do this by letting you easily change the sound for just one side of the split; others do it by letting you save LH+RH split combinations (which might share a LH sound, for example) that work with some kind of seamless sound transitions so you can switch the combi in the middle of a song without cutting off held notes. So some 61-key boards that I find more usable than most for split scenarios would be Roland Juno DS-61, Casio MZ-X300/X500, Korg PA700/1000. I'd still rather have more keys, though.