The Guaranteed Final Value figure or balloon payment to purchase the car will make a difference too. The figures given that the SLK is half the price of the 370z, but what are the deposits, what are the starting figures, are the terms comparable and what is the final figure stated to purchase the car?
It's all well and good saying that £250 a month for an SLK is better than £450 for a 370z, but what if at the end of the deal you need to find £20k to purchase it Vs £10k to purchase the 370z, as the extra money per month as been spent reducing the balloon figure?
The monthly payment figure is only one variable out of many that needs to be considered.......