Everything Apple (the Mac heads thread)

Any USB3 compatible drive should work if you have a usb to USB cable (for iMac to hdd) and USB to usbc (for hdd to Mbp).
We use G-tech ev 1tb drives (about 90 quid or 120 to come in a waterproof /dropproof case) but any drive should work. Might want to format using disc utility on the iMac and then transfer something small like a word doc across to see if drive format works on both machines before you copy everything and then find you hit a brick wall. Alternatively consider saving it all to a cloud service and just let it trickle across over time when they're both switched on? 40 hours sounds like you're uploading to the internet and back again - could probably sort some sort of local network and use machine speeds but @Velocio is your boy there.