what to do what do to

I am unsure how best to proceed.
I have another quote now from Diamond for £464 however my Direct Line insurance on my current car does not expire until July sometime.
DL previously wanted £76 to change my insurance over for the remainder of the period. I then realised that I hadn't informed them about the R32 skirts or rear valance...this then jumped to £135!!! ridiculous

I think for a non performance mod. This covers me from 14/03 to 15/07 when my current insurance runs out.
Anyway my dilemma is whether to now just cancel my existing DL insurance on change over and thereby losing any no claim bonus associated with 2007/2008 insurance OR to keep it on and pay them the eye watering change over costs. Does the additional years NCB from year 5 to year 6 make much difference in quotes? if I am getting quotes of £464 with Diamond now, how much cheaper would I get if I had 6 years NCB?
DL say they cant and wont tell me how much my insurance would cost for the new car in total for the year, if they are as high as (£460 (A6 current car) + £135 for 5 months with the cool GTi + circa £135 estimated for rest of year) then they are likely to want about £730 to insure me next year on my GTi.
In which case I should just move now to Diamond or other best insurance quote and thereby not gaining any ncb credit for 2007/2008? Think I have just answered my own question lol....bin Direct Line and go with the best and cheapest option.

Anyone see any reason not to?