Thanks for the advice everyone. I just test drove the 550 again and it's really nice and smooth but I'm still contemplating because the 535 has really low mileage. If I did get the 535 and felt it was not enough power it would still have good resale value because of the low milage and I could just trade it in for a 550.
But I will take everything I've read into consideration. And post picks of the car that I get
Thanks everyone.