When I enquired about a 200cpi cat I fould they are a lot cheaper than the Vx standard cat. I have done a post about this before but cant remember prices now. I think the downpipe with standard cat was about the £700 mark???
Treat yourself to a 200cpi cat. You may get asked to sign a declaration that you wont use it on the road. My 200cpi cat passes the MOT every time thou, so as long as your sensors and everything is working ok you should have no worries.