Print bigger

Extra cyan does practically nothing as stated above, but dialing in more of both magenta and yellow will slow the exposure and allow you to keep the same contrast. You can also put an ND filter on the enlarger lens or sometimes in the enlarger (e.g. if it has a filter drawer).

And don't be afraid of the f/16; the diffraction should not be visible to the eye in an 8x10 print and you can verify that yourself pretty easily.