Done five. It makes most other races look easy; last time I did it was a fairly tough year. There were quotes in Seahorse magazine from the Volvo Round the World racers (five of them did the race that year for practise) that it was tougher than any part of the RTW, and the owners of Sunstone (four times British offshore racer of the year, winners of the Cruising Club of America and Royal Cruising Club awards for cruising Alaska and Cape Horn) wrote in their blog that the seas were the worst they had ever met.
I stopped when the little boats largely stopped racing, partly for family reasons. With the introduction of the 2H division and the growth in 33-36 footers sailing two-up I'm seriously considering taking our boat down in a couple of years, if it passes the stability test without too many modifications. The switch to two-up racing takes emphasis off the boat and back on the sailors.