That old chestnut again,
forget Remus straight thru' pipes unless its just noise that you want. IMO, a decent 2.5" cat back system is a MUST! 200cpi cat, precat removed. If you want to spend some money, go for a Piper 2.5" S/S downpipe which includes a 200cpi cat and no precat fitted and then you could also go for the Piper 4-1 tubular manifold. You can buy this seperately over a period of time or buy all at once to the tune of around £1200 for a full system from front to back.