Thanks for all the comments guys!

The only thing that worries me a little is what Voyager said the last thing I want to do is loose bottom end torque, I was planning on removing it from the last two cats, so I'd still have 4 cats (which we all know are very restrictive).

I think I might take them off a few days before I go to the track and drive around & see if I notice any gains, (I'll probably think I am due to it being so loud lol)