When the Stealth R (Slightly smaller than a full on F16) was first produced it won the UK Catamaran Racing Associations Long Distance series. I think that included five long distance races and completed against F18's, 20's and Tornado's. I've competed in the 50 mile North Wales Raid , 80 mile Fast Cat Round the Isle of Weight Race and 50 mile Carnac Raid and won the shorter 25 mile Gower Challenge last year beating an F20 by 96 secs on corrected time.
From a personal point of view the only difference in dong this type of racing in a F16 compared to bigger Cats is that you have to concentrate that bit harder and it's probably slightly more of a physical challenge as well. A part from that it is very doable and very rewarding.