^^^ lol sick video..
That said, the BMW is lighter then the Audi. 50whp is 50whp and B5 S4's have an uncanny advantage on power under the curve and very good gearing.
That said, for street cars and mostly in the import scene S/C kits are a waste of money. They take power to make power, they generate a lot of heat and in some applications provide difficult to cool the intake charge depending on the setup.
Just look at that slow ESS S/C'd E9x that was running at Eurofest this year. That thing was running times a stock E9x would be running. That's a prime example. Or compare say a S/C e46 M3 to say an HPF turbo M3. The turbo car is always stronger.