Hmm, depends what the power is for.. Is it for the drag strip where 4wd grip is important, or for a high powered track day car?
If the latter then you can get away with FWD and nicely setup motor with LSD, big brakes etc. And as your changing out the K03 or the K04 for big power, then it's pretty much redundant if you start with the GTI (which you have) or lose money on the change up to the K04 S3.
Of course if it's the former and 4WD is important for the strip 0-60's 1/4 etc., then grab an S3 for ultimate times.