Tilling has a lot to do with the type of soil. My friend has soil that he has worked for years,barely a rock in the acre garden. The plow rolls it over full height like butter. My property on the other hand isn't that easy.
My point is that the engine speed of the 8n has a direct relation to the speed of the pto so trying to till a hard area that's never been tilled before might not be easy and trying to slow the tractor down will slow the pto. Now running an 8n with a tiller on it in my friends garden might work although we've never tried it.
Probably the best thing to do might be the rent a tiller to try on your 8n before you buy one. This way you're only out a rental fee instead of the cost of buying a new tiller. If you get a deal on a used tiller that you can sell at a higher price than you paid for it if it doesn't work out for you may be a way to go, but buying a new one if it doesn't work out will be hard to recoup the money.
Kirk