I have a 06 XKR with 75k miles on it. I'm going to replace my stock Exhaust System with XKs Unlimited over the Axle rear Mufflers delete System (Arden Type I think). I'm also thinking to replace the Cats at that time with Name less Performance Cats. Should I replace the O2 Sensors at that time or how long are they suppose to last. Also when should the Spark Plugs be replaced and what's a good performance upgrade Plug.

 

plugs are 60 k miles?

I change O2 sensors on my cars when I see my smog values go up dramatically.