I'm familiar with both and have used both for my in-office backup board at the church where I'm on staff.
Obviously, if piano is important, then the V80 is better - "LIVE" piano voice + 76 keys. It's more piano-centric, whereas the E423 is more synth-centric.
Other E423 vs. V80 differences:
1. 700 voices-including world voices vs. 500 voices
2. USB to Host vs. USB to Device-instant playback from USB
3. 174 styles-including world styles vs. 165 styles
4. 2.5 watts per side vs. 6 watts per side
(however, the E423 seems to put out more dynamic volume levels)
5. 150 arp patterns vs. 'intelligent arpeggiator' with arps matched to individual voices.
Exclusive to the E423 are the 2 live control knobs for arpeggiation and filtering - which add versatility.
Hope this helps.
Tim
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Tim Schaeffer
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YAMAHA CVP-509 / Korg Pa300