First of all, a C-17 is by any measure bigger than a C-141. Both planes have unlimited range with in-flight refueling.

C-17 General Characteristics

Primary function: Cargo and troop transport
Contractor: Boeing
Power plant: Four Pratt & Whitney F117-PW-100 turbofan engines
Thrust: 40,440 pounds, each engine
Wing span: 169 feet 10 inches (51.76 meters)
Length: 174 feet (53 meters)
Height: 55 feet 1 inch (16.79 meters)
Speed: 450 Knots (Mach 0.74)
Maximum takeoff weight: 585,000 pounds (265,352 kilograms)
Ceiling: 45,000 feet (13,716 meters)
Range: Unlimited with inflight refueling.
Crew: Three
Armament: None
Unit Cost: $180 million
Date deployed: 1993

C-141B General Characteristics

Primary function: Cargo and troop transport
Contractor: Lockheed
Power plant: Four Pratt & Whitney TF33-P-7 turbofan engines
Wing span: 160 feet (48.7 meters)
Length: 168 feet, 4 inches (51 meters)
Height: 39 feet, 3 inches (11.9 meters)
Speed: 500 mph (Mach 0.66)
Maximum takeoff weight: 323,100 lbs (146,863 kilograms)
Ceiling: 41,000 feet (12,496 meters)
Range: Unlimited with in-flight refueling
Crew: Five
Armament: None
Unit Cost: $40.9 million
Date deployed: May 1964