S4 or RS4, just from a handling point of view

Hi, I know that the S4 can be mapped to perform as well as or even better than and RS4, but .... do they use the same 4WD system and sports electronic or other type of diff.

I owned one of the original UR Quattro (D141KNW) and it handled better than any car I have had since. I now have the A3 184 Quattro but know that this is a very different type of setup and to be quite honest it is a bit of a disappointment and the chassis quickly ties itself in knots when pushed.

I am now in the market for an S4 or RS4 (I appreciate the S4 will be a newer model) but want the better handling car, so...... which one would it be?

Thanks in advance

regards

Does the S4 have the option of the sports diff?

Do they both employ the same 4wd system?

How does the sports diff work and is it necessary for spirited road driving?

Regards