TO say all tractors need WOT is like saying all cars are built the same and can run 60mph at the same rpm. Not true..
Look at your tractor and determine what is required for 540 RPM (unless you have one of them fast pto's). Anything further than that with the throttle is just easting fuel. My Kioti is 2500 rom to reach that number.
Many tractors have a mark on the tach gauge that identifies the 540 rpm.
I have had my used "caroni" looking tiller for about 16 yrs now. I paid for $300 for it around 2010-2011 replaced the tines immediately (agrisupply) and till up the garden every spring, summer and fall planting.
That's not exactly what I said . . . just trying to make the point that a little faster is ok.
Think about your old push mower. Did you ever run it at anything other than WOT? Did it matter to you to know EXACTLY how fast that blade was spinning. Same with a walk-behind tiller -- don't you just push the throttle all the way up and let it do its thing? You don't need a tachometer or worry about over-revving it. No one worries about "tine speed" or "blade speed". Fastest is best.
With a tractor mounted tiller or mower or snowblower, it's the same thing. If you're mowing with your 3-point mower and running it at exactly 540 RPM (according to your tach), you're not getting the best possible cut. If you can run WOT and get another couple hundred RPM, it's going to cut better. And that's not just wasting fuel -- that's doing more work and doing a better job in the same amount of time.
Same with a tiller. You're not wasting fuel. You're just spinning it a little faster and doing more work with it in the same amount of time. It's not such a precision tool that it needs to spin at exactly 540 RPM on the tractor end of the PTO shaft. Nothing is going to fly apart just because you budge it up another few percent.
With a baler or haybine or implement that changes direction, you can usually find a range where it runs smooth, but beyond that it shakes and vibrates a lot. Not so much with a tiller or mower that's balanced and just spinning. My 30 HP Kubota does best at WOT (2700 RPM, I think) with a 5' tiller. Running it at exactly 540 RPM (closer to 2500 RPM) would not save fuel and would just take longer to do the same job.
To further complicate this, do we set the RPM / throttle BEFORE we lower the tiller into the ground or AFTER? Once you drop it and load the engine, you'll lose a few RPM. Do you compensate as you go? Might as well just run it wide open and then manage the load with your ground speed.
Not trying to argue the point, just my opinion. Some things like boats and mowers and tractors with tillers attached are actually meant to run at WOT. And there's no reason not to . . .
Tine speed would depend on belt/pulley or gear ratio from 540 rpm to rotor/tines. As far as I know, they are reduced down. 
