£1100 a month isnt bad then, my zed costs me £900 a month and thats without any loan. Its scary how much things soon cost. Things like petrol & depreciation are the main killers.
One thing I wondered was whether its just worth hiring a decent car for weekend use as if you only plan to use it occasionally as a 2nd car it may work out cheaper.
What are you accounting for in your £900?
MOT, tax, insurance, servicing, 1 set of tyres, depreciation of around 2k/year (i.e. everything it costs you to use the car on the road for 12 months), works out at £450 a month for me. I do a lot of miles (about 450->500mile a month), so the remaining £450 is fuel for me to get to work/back each month. Obviously if its just a w/end car the petrol costs would be less. In your example, £300.
So thats not a like for like comparison then is it.
In my example I never included MOT, Tax, Tyres or depreciation. All of that on a GTR with your mileage is likely to increase that monthly cost by about £800 or so (£2k service, £2k tyres, £5k depreciation, £400 tax annually).
So, it would cost you circa £1,900 a month compared to your £900 a month 350z when compared like...............
£1900 a month is a lot of money to be throwing at a depreciating asset like a car, not when a lot of people don't even take home £1900 a month from their salaries....