31st May just there as in 7 weeks ago?
I reckon you would lose a fair chunk of cash.
Taking your car out the equation just now you can get a 3dr manual 7R for £26,881 from DTD
If you use the VW configurator calculator, it recommends a deposit of £3082 on a full price R. So if you add the discount from DTD which is £3,857 to the VW recommended deposit your £60 short of a £7000 deposit.
So putting the £7k as a deposit you'll be £354 a month over 36 months. That's obviously with you adding £3k of your own money.
You still have to pay off your old GTI. I wouldn't imagine you would have an equity on it at all despite putting £3k down.