Right after a chat with my mechanic he said if i take off the cone air filter and replace with a standard one and take off my ****ty loud exhaust that has NO cats on and replace that itl help the car a hell of a lot, my question is when i look for a new exhaust whats the difference between a sports cat and a standard cat? want the car to be pretty standard underneath now as the huge roar is doing my head in on long trips

 

To be honest noise is more to do with centre section and back box in my opinion, but decat will obviously up the volume a little.
If I was you I'd get a decent panel filter, prodrive sports cat off an sti and decat the rest. You'll probably need a remap to make it all spot on, might as well add a prodrive back box as it has been said to be on the quiet side.

Difference between Decat, sports cat and normal is level of restriction with Decat on the wrong side of legal regarding emissions. Beware of some sport cats as some are useless.