I've got a remus centre section and the original irmscher letter box exhaust on a Veccy B SRI 150.
You can hear it sounds a bit different from the inside of the car (a little bit noisier, but not in an annoying way).
It definately sounds better from the outside of the car. Not too noisy, bit like a touring car I suppose.
It certainly sounds nice once you rev past 4000.
I guess it possibly pulls a little bit harder when reved hard. Nothing too noticeable though.