...what i would like to know is how does the A3 2.0T quattro compare with an S3? handling wise? is it the same as the S3 apart from the engine? or are there other things on the S3 to improve the handling etc? i know the S3 has the KO4 and uprated fuel pump/injectors etc (correct me if im wrong) but i have read about people making modifications on the mk5 GTI to the handling by using some S3 parts?
As I say, I've owned both. The 2.0T quattro will usually come in S-Line trim, but is / was also available as an SE - either way, it's an engine available as part of the "normal" A3 range whereas the S3 is a model in itself.
I was very fond of my old 2.0T quattro and I think it had aged very well when I sold it at 5 years old. They are very nice cars and age well in S-Line trim, with some options and a nice metcallic finish.
You have to remember that a 2.0T will come in one of two trim lines (SE or S-Line) and, along with all other A3s in the same trim line, will have been optimised as an attractive and reasonably comfortable car. In short, it wears a very similar mechanical spec whether it's in 1.6 105bhp or 2.0T 200bhp form - and you won't find significantly better brakes, suspension etc other than what comes with the trim line. To be fair, the quattro cars get their own suspension settings and other minor mods (and you could argue that a Golf GTI doesn't go very far over a GT), but the work is really aimed at finessing a good all-round car rather than creating a performance model.
The S3 is developed as a separate model line and while, yes, you can swap some parts around - it's a lot of effort to make an S3 out of a 2.0T quattro. My S3 drives very differently to my 2.0T quattro and it's not always better. Around town and for family duties, the 2.0T gives access to its torque at lower revs and is a smoother drive under 2,500rpm. The bigger K04 turbo of the S3 makes it feel slightly less rounded in character, but is significantly more rewarding at higher revs and when driven with vigour.
I'm running out of puff now, but I'd just add that the S3 handles and brakes a lot better too. In short, you could get to a similar power level to a standard S3 with a 2.0T, but you'd need to go a lot further to re-create the full experience.
remap time!! mine is on the way 
