It's definitely a thought.
To be honest, going for £8k would leave £2k off the finance, giving me some freedom to use savings (or create some!) for repairs.
Just threw some figures, and taking everything as bad as it can be, a 350z works out at £600 a month (this is including finance, fuel, tax, servicing, insurance etc).
My current car comes out at £250, and as I say, I have a bit of cash left over (as well as a pay rise coming, and a girlfriend coming home).
If I can be sensible and put this off for six/seven months until she's home and things are stable, it's most definitely doable.
I think this answers your question for you. Leaves you very little for any unforseen problems & also enjoying yourself. I think it could spoil the experience for you if you found yourself very tight for finances. Give it the 6 months & reassess then.