I guess I dont' know what valve float is, then.

I thought "valve float" was when the engine is turning so fast, that the valve doesn't have time to close - it actually lags the bump in the cam that caused it to open. This would cause intake and/or exhaust flow in and out of the combustion chamber to be "ragged" or whatever term you use.

Meaning that the engine would not run right, would not deliver power properly, and would self-limit it's speed.

I don't see why the engine would lock up!?!?!!? Are tolerances close enough that you have valves and pistons hitting each other at this speed? Or am I just not getting it?