If you want to keep it long term then maybe don't do a PCP?
I tend to do mine on a straight refinance if keeping it long term, 72 month straight repayment. I know 6 years sounds like a lot, but I prefer to know at month 36 or month 48 that if I want to keep it I just keep paying for 2 years more and it is mine, I don't have to worry about finding £17000 or £12000 or whatever the final payment may be.
The C220d AMG Line with auto 'box and the Premium Plus pack is £32k from most brokers.
So a saving of £6k.
With your £5000 down that you would pay on Agility, you would pay £430 a month with a straight repayment, so more money each month, but better to own it after 6 years than get to year 4 and have nothing, or have to find £12000.
Actually, without the prem plus pack it is £28800, and £382 a month, so £20 a month more but yours at year 6.