The A4 is a sort of heavy car w/AWD. A Mazda 3 is definitely going to feel more spirited considering how light it is, and only having to put power to 2 wheels. But the A4 is a tank and drives like it's on rails compared to most other animals. It might not be really fast, but you could "outdrive" most cars. The engine should still have near perfect compression even at 200k. A chipped 1.8t gives around 200hp but the torque is really where the big difference is. A 1.8t will require a little bit more tlc, though. Don't be discouraged if you test drive a stock 1.8t, it'll be quite slower than the 2.8. It's a dog, actualy.

Legacy is cool, too. I think the previous generation like you are looking at is more dated than our 3 generation old A4s, though. I've become a big Subaru fan lately... My wife has a B4 just like this:

 

Here is mine :