If you extend the question to Rally Raid the biggest must be Dakar 18 (slightly bigger than Fuel AFAIK). The overall map size adds up to 15,000 km², it's hard to say how long the individual stages because the distances shown are scaled up but most take somewhere between 30 minutes to just over an hour to finish.
(Don't read this as a recommendation to buy, some people love it, some people hate it).