I've consulted JonnyC about most mod's on my car (from when he had his S3) and what he doesn't know about the 2.0TFSI now after all the work his done across three cars, well frankly, isn't worth knowing.
I've spoken to him about exhausts and yeah, of course a full system will give you the best results, but I need may car to appear relatively stock for when i'm visiting clients... plus the boss (AKA my girlfriend) would have a word with me about something like an aftermarket exhaust.
Anyway, with the new facelifted S3, lot's of people have had issues with misfires after having remaps done... nothing new, as a lot of people suffered injector issue related misfires, but on the facelifts the injectors were not the cause. The downpipe is slightly different on the facelift S3's and this was the cause. Basically, it is the most restrictive part of the whole OEM system on all 2.0TFSI cars (when you see it next to the Milltek you can really see the difference), and the OEM backbox is pretty free breathing anyway.
So, I put just the Milltek downpipe on as a bit of a test to see if for 40% of the cost, you can get 70% of the performance gain and you guessed it, Jonny was bang on the money I've seen an increase in headline figures of 7bhp and 6lb/ft, but that is only part of the story.
Here is a comparison from when my car was just a map and panel filter and then adding the down pipe:
You can see low end torque is much improved, and power is pretty much improved all through the rev range.
You can definately feel the difference, plus the exhaust note is improved.
I'd recommend this as a cheaper alternative to a full system and it will deffo yield more performance gain than just the back box.
J