If that were accurate it would explain why I prefer the stock cam over the 261. I do disagree with it going all the way to redline as over 4.5-5k the cam just falls flat on its face.
Can I assume that you have checked out other possible causes for your engine to "fall flat on its face" at around 4500 and 5000 RPMs? Or.. are you convinced its the 261C cam?
Have you talked to Tod or Ted at engbldr?
How many miles on your rebuild?
Are you planning to change the cam?