I sail an infusion and raced at 385 at Canadian Nationals... we were competitive in everything and usually in the top 5 in the light air on the last day.
I was a little hesitant to race at that weight but the only time I felt it MIGHT have slowed us was downwind... we went from right behind the leaders in 2nd to 4th in one downwind, I really felt they were pulling away a little bit but that just could have been us sailing poorly.
We raced at the same weight as on the N20 and I feel the Infusion handles the weight just as well as the 20 and it really pays to have a fatty on the wire downwind in waves and you don't get that stupid beam slap like the 20