Uncle Dave.
I am thinking of getting the Pa3x. My thoughts are for the difference in money I am going to go with the 76 keys. I found this info on a Korg forum.
Keyboard:
61-semi-weighted keys with velocity and aftertouch

76 semi-weighted keys with velocity and aftertouch

Hard Disk / Mass Storage
Standard 4 GB memory USB

Optional 2.5" SATA Hard Disk Driver (61-key)

Standard internal 2.5" SATA Hard Disk Drive (76-key)



Display
Pa3X 61: Resolution: 320 x 240 pixels - TFT Color TouchView Graphic Touch Screen;

Pa3X 76: Motorized Tilt Display - Resolution: 320 x 240 pixels - TFT Color TouchView Graphic Touch Screen


Dimensions (W x D x H)
980 x 366 x 145 mm / 38.58 x 14.41 x 5.71 inch without music stand (61);

1192 x 366 x 145 mm / 46.93 x 14.41 x 5.71 inch without music stand and with the display fully lowered (76)

Weight
14.7 kg / 32.4 lbs (61); 17.5 kg / 38.58lbs (76)
Its only a matter of 6 Lbs. Hope this helps. RC