Another option would be to take 190 and then drive down to Badwater Basin and back to Furnace Creek. That would be somewhere in the middle of the two options for time. It's a short bit of backtracking, but you could take Artists Drive on the way back up to FC, although it would take up a bit more time it's part of the 'sight seeing' and Badwater and Artists drive are a big part of that. Get an early start and you will be fine !

My advice would be to stay around the speed limits as it's not worth risking a ticket or worse. They do have spotter planes flying in the desert areas who can ticket you without you knowing it, until you get the bill ! One of the toughest parts I found was after driving at 60 +mph for a long period on empty roads and then entering town with a limit of 25mph, it felt like we were going at snails pace, but it's when we entered thses towns we saw the most [only] speed guns pointed our way.