Haven't got either, but I'd say probably...

a) if you want 76 keys, yes (no-brainer!)
b) if you use the harmonizer a LOT, yes (better on the PA1X - more options)
c) if you are into sampling, no (PA800 loads faster and addresses more RAM)
d) if you worry about polyphony, no (far better polyphony on a PA800 - you'll need it for that great Guitar Mode styles, I've heard)
e) if you use a grand piano sound a LOT, no (PA800's is MUCH better)

Your choice...