You may want to go over the specifications list of both of them and decide if the feature difference is worth the extra cost of the Pa2x. Check out the sound demos of each one also. To me they sound pretty similar from the .mp3 demos on Korg's web site but of course the only true test is a personal hands on demo of each keyboard yourself.

Pa2x specs

Pa800 specs

$2,699.00 for Pa800 61 keys

$3,550.00 (approx.) for Pa2x 76 semi-weighted keys

= your decision based on your needs...

Best,
Mike