The elephant foot adjusters on the SOHC cannot handle high rpm - over 6,000 - for very long. The problem is the flat foot scrubbing across the valve stem/ lash cap eventually squeezes out the oil film. The resulting heat burns everything up. High spring pressure makes things worse. I've shown that you can wreck a new adjuster in less than 2 minutes sustained at 7,000 rpm.
The non-adjustables with their curved tip surface are far better at keeping the oil film intact. (The old-timers knew this, and never ran adjustable rockers at the drags.) Better yet, Barry's roller tip rockers are da bomb!