Ive got the K&N panel filter in my GT TDI 140 , didnt notice a major difference to be honest , perhaps a ever so slightly increased throttle response and bit deeper sound.
I was once told to stick with panel filters on TDI's as full induction kits are a bit pointless apparently , plus i wouldn't want to destroy the diesel sound , i like the raw'ness of it
I could be wrong though...