In Acrobat Reader, I did a "scale to fit printable area" on 4×6 inch index cards. One side is grid and one side is blank which turned out to be quite handy for this experiment. Shown with a regular size Pilot G2 pen for scale.
Lefties can simply smurf the other side of the page. Those using anything besides the Circa/Rollabind system can still do this and hole punch the index cards for a handy & portable DIY calendar.
Why 4×6 cards? 3×5 seems too small for me to have a reasonable amount of space to write and also I’m fairly sure my printer doesn’t handle printing on 3×5 cards. People with a printer than can do 3×5 cards should be able to scale down to that size and still get a good result.
Using a top-bound hipster PDA (such as the Circa PDA?) Just rotate the card 180 degrees and the print so the big blank space would be on top. I think that would work 🙂