Steve,
The E-50 & 60 don`t have a vocal harmonizer , and I don`t think it displays notation , the E-80 does.

If your looking for the best song writing tool , then you might want to consider the Motif XS6 Synth.
You will need a computer with notation software.

The other route is the Tyros 2 , same great FSX key-bed as the Motif , but it displays both lyrics and staff notation and has a vocal harmonizer.

The T-2 is well made but getting old and might be replaced later this year , no time frame has been given.

The PSR-S900 has most of the T-2 features , but lacks the build quality , you lose the FSX key-bed and quality control surfaces. But you will save almost 2K.

The Pa500 has no vocalizer and does not display notation , lyrics I`m not sure , the Pa800 only does lyrics and not staff notation .

So by now you must be fairly confused , misery loves company !! LOL
Welcome to the world of arranger shopping !!

I hope I have helped , best of luck !

Gary 