that's fine but all kinds of things can cause the 'best setting' in practice to vary a little from that. For example all tyres have a slip angle characteristic and this is usually a non-linear function with loading (vertical and lateral). This means that the best setting will certainly vary with tyre type and may even vary with road speed too. In extremis it may mean that what looks like perfect Ackermann geometry (in theory) doesn't work as well as it should in practice.
If you try a different toe setting and you prefer the way it steers, the practical thing to do then is to do some 'corner coasting' tests with both settings and this should tell you if one setting is scuffing so badly that it affects your speed or not.
Lots of trikes and HPVs seem to have 'bad steering' in that they scrub badly in sharp turns, enough to slow noticeably. Fixing this can be problematic.