If you went over the agreed mileage and wanted to hand the car back at the end of the term you would be hit by excess mileage charges as well don't forget. You might well go into negative equity even on a trade-in if you have grossly under-estimated the annual mileage. You will probably be fine on a private sale, but as I said you won,t have much left over by the time you have settled the balance.
I opted for a 3 year pcp with 12.5% depo to keep payments under £500/mth and keep my options open in 3 years (balloon is about £17K). so I opted for the higher depo
i will have enough equity in 3 years for approx. 10% depo deposit on another car
if I keep it then it would be cheaper than any other 3 year old car
if I hand it back im sure I wont pay anything other than usual wear and tear and excess mileage
if I do £1K depo then it limits my options if the rest of the depo is added to the balloon or increases the monthly payments way over £500/mth - therefore as I may as well keep it after 3 years