Tom, I've got the Race Tech "gold valve" fork kit & springs on my Suzuki Bandit. Made a huge differnce. I was surprised they offer no kit for the Guzzi Marchozzi forks. I've never heard of ATK cartridges, can you elaborate or cite the thread?
Having said all this, I am pretty satisfied with my V11 Sport "as is". Seems to handle very well. I'll say one of the best bikes in the curves I've ridden. Mine has as handle bar conversion which provides good leverage. I've not touched the set up since I picked up the bike in August.