from what i have been told, a stage 2+ ED30 will feel/be quicker from 30-100 than an S3.
Just look at the review for the new leon cupra 280 vs the golf R, they said the cupra was more fun with it being FWD.
Only you can make the decision mate, if you put the car back to standard you'd be able to sell the bits that came off it.
I was thinking about this the other day, I've spent nearly 1.5k on mods for this car so far, that's 1.5k I could have put towards an S3, but at the end of the day I am happy with what I've got and to make an S3 be as powerful as this, it would cost me more money too