Direct answer: Eagle rates the 1/2 HP Eagle 2000 FR for a gate up to 45 feet and 1,000 pounds. The 1 HP FR version is also rated to 45 feet but raises the weight capacity to 2,000 pounds.
At the maximum, details matter more
A 45-foot gate is at the published length ceiling. Gate condition, rollers, track alignment, wind exposure, and actual weight deserve more scrutiny than they would on a much smaller gate.