If you don't need seating for seven (and seven people + luggage won't fit into a 7-passenger Explorer) reserve the 5-seat model. If you see something better on the lot, your readiness to pay an added $150/week is powerful negotiating leverage.

The upgrade you want is the 24V (yes, 24) V-8 engine with 6-speed auto in place of the asthmatic V-6 and 5-speed. Look for the V-8 badge on the tailgate. Difference in fuel consumption is entirely minor.