Not denying either of you right in what you are saying my point was that they are two different tyres he is talking about, old Avon cobra and the new Avon cobra chrome.
Was on advice of the bloke who's going to tune it, but also seems pretty common. Stockies get maxxed out easily (they're the same size injectors as on a stock 103cu TC, and cammed M8s are generally putting out 120hp easily) and even 5.5s can get a good workout, so going up next size just keeps duty cycle down.