I would think the heavier the steel valve the more the difference. A 2.05"with a 7mm stem won't see a big a benefit as a 2.40" with a 11/32" stem. Also in the equation would be cam design, spring and retainer weight, rocker and pushrod stifness. The better the valve follows the lobe with these items, the less gain there will be. I've had good succes to 7200 with T&D 1.7 paired rockers, Trend 7/16" x .165"tapered pushrods, Pac Ti retainers & their 1124 spring using Ferra 2.25" x 11/32" steel valve. The cam profile is pretty smooth. Comp RX 1718 int lobe, XCX1862 exh lobe. Zero failures. Springs last at least 300 passes (Hardcore has tested them)
Doug