I'd looked all over for that - thank you. I make that a 900m grid versus a 280m grid. Clear enough, and whilst I can see the appeal of the finer grid, I hope that I don't do any flying that would justify it.
This all, for me, does seem to be homing in on the 500, with the better screen but not expending money on the nice but unnecessary fine grid. And probably a spare battery - since I know that I will fly quite a few aeroplanes without easily accessible power, sometimes on long trips.
G