What is the most POWERFUL engine you have ever been behind?

Buddy has a 71 Challenger with a stroker hemi, dynoed at 550 hp/550 tq, 727 and 4.10s.
My brother has a 70 Chevelle SS 454 stroked to 496, 550 to 600 hp, 200r4 auto with 3.73s.
Both pretty fast, but the Chevelle is a little better balanced than the Challenger and feels much better to drive.