Frankly I don't know _what_ that chart is all about. What I pay more attention to is the formula: (1/2R)(rpm)=fpm. IOW, take half the radius of your wheel, multiply by your motor rpm's to get feet per minute that the face of the wheel is travelling. I believe you want that to be about 5,000 to 7,000 fpm.
It's a tradeoff. I have an old 1.5 hp motor I use at 3600 rpm. An 8" wheel is perfect, providing 7200 fpm. I tried a 10" to get the face speed up, but the extra leverage makes my motor bog down. So although I get more speed, I lose the ability to put pressure (and heat) on the work. A newer motor of the same hp might work better in my case.
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