I have a jaguar xf supercharged 2012. With dunlop 255/35zr20.

1). I have a few questions first off how often should I expect to be replacing these tires?

2). Do I really need these high-performance tires? And if not what would be a suitable replacement.

 

Both questions depend upon your style of driving, about which we know little.

How many miles are on the tires now? You can research them on TireRack (customer reviews) to estimate longevity. And high-performance tires aren't necessary for most of us but some swear by them. I will say that with such low-profile rubber (which is required with your 20" wheels) you should be careful about driving on substandard surfaces. Both tires and wheels are vulnerable to potholes and such.