RTCC just fitted the 4 pipe Librands pipes to my MKI the improved the sound and whole feel of the car tremendously I also drove the MKIII with side pipes while picking mine up there is a totally different feel in the car as you can hear just 4 cylinders at a time although I think that there is a little more base, I think that as a driver the rear pipes sound better. Both rear and side pipes are quiet at idle it is a trate of the BMW engine however the both sound good as the engine is reved up.
The sound aspect for someone not in car is similar it is not as rude as a TVR because it idles so quietly but has a very British Spitfire sound when pushed I think that there is a change of pitch as a side piped car passes as you go from hearing 4 to 8 cylinders. I do think that the loud version of the rear pipes is nice but if you plan to use the car on a track I have heard that they can push the usual noise limits close, they are also nice when you first get in the car or for the first few times you drive it but I am not sure if the sound would not be a bit too much on longer trips or for every day use.
