It would be worth contacting the manufacturer and asking what clearance would be needed. But personally I'd scrape back at least a 30mm clearance to allow for heat from the light. I'm not entirely sure why insulated plasterboard was used in a ceiling with a warm room above?
They are over power for the job, they do a 7w option too. But its too late now you have the holes. The 10.5w option is designed to be used with a dimmer. I have 4 x 4w in one of my bathrooms (8ft by 9ft) and its way over kill.
I will be changing my halogen spots in my open planned kitchen soon. Maybe I could use the 10.5w there and get new 7w for the ensuite. There isn't much to changing them. Is the 7w ip65 aswell for above shower areas