honestly, I wouldn't bother with the TQ, as much as this is going to annoy people, it's a really pointless car. (sorry TQs boys!)
It's got all the weight of the S3, but none of the power. You don't get the bigger brakes, you don't get the quick rack, the cast wishbones, the hubs correcting roll centre, you lose all the stuff that makes the S3 worth while.
the S3 in standard 210/225 form is pretty slow, a quattro with a ko3S mapped to 225bhp will be quicker than the S3, due to the higher torque, but still nowhere near as quick as a FWD ko3S car due to the extra weight (200kg) of the quattro system. It also won't handle anywhere near as well, due to the lack of Hubs/rack/wishbones/brakes
If you're going to take the hit on the weight of the quattro, then you really need the ko4 turbo to go with it! S3's can be picked up from £4k now, and it really is a lot of car for the money.
That said, I also don't understand the stigma that you can't get the power down in a FWD A3, I run two FWD A3's, both with 225-230bhp currently, and I don't have a problem getting the power down at all in either of them. They're also far more interesting to drive than the 4wd counterparts. I'm about to upgrade my FWD track car to around 300bhp, and to be honest, I don't forsee too much trouble in getting that power down either!
Sure, in the wet you're going to struggle in 1st gear, and sometimes second, but anyone who's wanting to go flat out in the pouring rain is foolish anyway, quattros still have the same number of brakes as the rest of us! I'm fairly sure owners forget that.
Given your position now, I'd either modify the FWD A3, or if you want a change, which it sounds like you do, spend the extra and get an S3