He's actually not the first person to do it...someone who used to post on here did it with an otherwise stock engine and posted a video. You could hear the valve floating as the RPM's came up.
I figure this...that much rotating mass spinning that fast...even with upgraded valve springs, you'll get away with it for a while, but sooner or later things are going to scatter. There's a reason why big truck engines generally don't turn above 2500 RPM or so (and cruise closer to 1600 RPM IIRC), and the engines in large cargo ships barely crack 100 RPM. A person can do as he sees fit with his engine, but I strongly contend that it's taking a big gamble for not that much gain. Longevity's important enough to me that I wouldn't even think about doing it.
JMHO...
What it is is piston speed. The larger the stroke, the slower the rpm generally. If you have a stroke of 2" at a certain RPM, and a stroke of 4", the piston/rod combo is going to be traveling at a much higher velocity for the 4" vs the 2" stroke. Those extremely large engines turning 100 RPM's do so because of this.
Ever wonder why formula 1 engines can turn rediculous RPM's? "Big-bore, short stroke: F1 V8 engines are currently limited to 2.4-liter and 98mm maximum bore, or 3.858 inches. That means the maximum stroke for that bore is just under 40mm or 1.566 inches." Short stroke = higher RPM.
IDI's have a stroke of 4.18". That means at 3300 RPM's the piston speed is about 38 feet per second (FPS). At 4500 rpm's it increases to 52.25 FPS. 4500 RPM works out to be 15.9 Meters per second. F1 Engines are in the 28+ MPS range. For many decades OEM engine designers considered 3500 ft/min (17.8 m/s) to be the threshold.
Now talk about the G force on the piston/rod. Think at the bottom and top of the stroke, piston speed goes to 0, and then halfway in the stroke it reaches it peak piston speed.
Chevy 350
Engine RPM/ Piston Velocity mph / G's exerted on rotating mass.
6000/ 62.20/ 1140.15