These are very high wind ranges for a lightly ballasted 21 footer. You do have a number of options short of reefing. First of all in that kind of wind you should only be using a working
jib (rather than a genoa as heeling is a part of the problem.) Next it is impostant to blade out your sails. That means on the mainsail, lots of outhaul, halyard and vang tension. It means a relatively tight mainsheet with the traveller eased to leeward. It means lots of backstay tension. At some point approaching 20 knots of wind, it will make sense to reef the mainsail. On a boat that size it becomes very important to be able to reef quickly and reliably on the fly. I strongly recommend that you have a two
line reef system lead to the cockpit and that you keep a first reef ready to throw in.
On the
jib it means moving the sheet lead aft a little, really tightening the halyard and lots of forestay tension.
On a centerboard boat you can raise the board a little to move the center of lateral resistance aft and further reduce weather helm (But this is not the best idea if your 800 lbs of ballast is in the form of a swing keel.)
Obviously getting weight up on the rail helps as well. Keeping the boat as flat as you can is important because on older boat designs as you heel the boat''s waterline becomes more assymetrical and morphs into a shape that tries to spin the boat into the wind.
Jeff