I should add that I agitate at a normal rate (10 seconds once a minute), but I do it very, very vigorously.
To the OP: really the best way to find the results, and grain character you like is to just buy a few rolls and try different developing regimens on each one. Pick the one you like the most and refine it from there.
Vigorous agitation will make a difference.
Mine are all done in a Jobo, so agitation is continuous but not vigorous.