Was slightly disappointed with my renewal quote from CCI after they made some changes to their policy (they now basically exclude any commuting) as it was £801, apparently £60 down on last year, but still a hefty chunk of change.
I called them up and they said the only way to bring it down further was to reduce the mileage allowance to 6000 miles from the 8000 they had quoted at.
To be honest, 6k is plenty for my use and I was delighted when the premium was further dropped to £647!
So as long as you do not need to commute in your GT-R and do restricted mileage, CCI are the best by a mile. Don't forget that includes 5 track days a year (by prior arrangement, and excluding the Nordschleife).