Comfort and speed are different
What is comfortable for you and your crew is subjective ...What is fastest (most efficient) is:6 knots True = 9 knots apparent, full sails and 4 degrees of heel10 knots True = 13-14 knots apparent, full sails and about 15 degrees heel12 knots True = 16 knots apparent, full sails and 17 degrees heel16 knots True = 19-20 knot apparent, full sails and 21 degrees heel20 knots True = 23 knots apparent, first reef and 22 degrees heelAbove 20 knots true, reduce sail to keep heel when close hauled to under 25 degrees.In 30+ a double reef and a 100% jib keeps the boat at 20-25 degrees heel and sailing nicely.These numbers are for a fully crewed boat. A full crew for a C30 is 1225 pounds of crew ... 6 or 7 175 - 200 pound guys. If you are sailing short handed you will need to reef much sooner ... the 20-25 degree rule should be your guide, there is no need to keep the C30 under 20 degrees of heel ... unless you or your crew is not comfortable at higher angles.