It's been a couple years since I bought it, so I couldn't remember all the reasons I went df64 over 54, but I just remembered that I made a spreadsheet of a few models I was considering. Looks like the main differences other than burr size are that the 64 has a 250W motor compared to the 150W of the 54. The df64 also has a plasma generator to combat static. I think 64mm burrs are also more common (not that I'm going to buy new burrs for a long time).

Also, idk where you are looking, but espresso outlet/turin grinders gives you a lot of money off if you pre-order. I'm not sure what the equivalent Canadian company is that buys pallets of them from whatever factory produces them, but that would probably be your cheapest bet if you don't mind being patient.