OP impressed by your scouring of threads for exhausts, not missing a trick..
I've been looking myself, budget slowly creeping up... Aiming to have an Evolve e- tronic, they do sound great
but the 20% off from Cutters sponsor although a good number still north of £1,700... Have to be patient..
Anyway there is a Milltek Back Box on eBay at £600 if you are considering your options - rubbish with links, but you'll find it..
Not endorsing this particular item/seller was just one I stumbled across looking for myself, was in my watch list...