Horsepower doesn't matter because you can not measure it and you can not "feel" it. Torque is what moves the car. Horsepower is just a mathematical calculation:

HP = Torque X rpm divided by 5252

The S4 does well because with the turbos all 258 pounds-ft of torque are available at 1800 rpm and held constant past 4000. The TL with less peak torque (238) has about 210 at 1800 rpm. Don't forget gearing (trans and final drive ratios and tire diameter) which favors the S4 especially in first gear and also in 5th and 6th. From 60 to 80 in 6th the S4 will walk away from the TL...at the expense of higher rpm cruise.

 

Again, another that uses formulas and has no idea of the concepts. What do you think that horsepower is? Just a calculation really? Try again.

Horsepower will tell you the engine's ability to change RPM quickly under load and it is exactly what you need to build speed or acceleration, from any rpm.

BTW, the SAAB 9-5 has as much torque (258 ft-lb of torque starting right from 1900 RPM.) as the S4, is lighter and not as fast. Even the TL is quicker with less torque. HP is more definitely more determinant.

 

Torque vs. HP?

While I agree with chadr (explanations), nextguardian (relationship and gearing) and princed (conclusions), Saintor is more into magic to me.

Torque vs. HP? It seems that there is not so much "vs." given the linear relation between them.
I use them only to describe two points from the engine's curve: the point for maximum torque and the point for maximum RPM x torque (HP).
If you want to compare two engines - compare the curves.

When is a car faster? Well, the engine shows the potential for being fast.
Assuming the same weight, you still have the gearing in the equation.
And the gearing is fitted different on different engine curves in order to get the maximum benefit.
So even after you see the engine curves and weights you cannot tell for sure which car is faster. Even less, when you only know two points from the curves.

But to simplify, assuming that the gearing is "transparent", and since the point of maximum torque will always be before (or coincide) the point of maximum HP on an engine's curve, I would conclude that the torque gives an indication on how "fast" a car is at lower RPM (lower speeds, on short distances) while HP gives an indication on how "fast" is a car at higher RPM (higher speeds, on long distances).
By "fast" I understand the acceleration you can use in the two different scenarios.

I would first look at torque when talking about 0 to 60 mph times and I would first look at HP when talking about races (distances).

 

I think if we all had a Thermal-Higajilator powering a Flux-Capacitor @ 1.2 Gigawatts of power then the whole HP-Torque issue would be mute!!

 

We had a 1988 RX7 Turbo way back when, rotaries have no torque they rely on RPM for horsepower and turbos made it worse.
The magazines reported good 0-60 times for the car, but the only way to do it was to rev the engine all the way up and then slip the clutch to avoid melting the tires.. The car smelled terrible if you did it... ok so I was young.
And yes I do race cars, I currently have an SCCA Formula car and the comment about horsepower at RPM being good on the track is so true. I have had cars that could barely get rolling but once the engine hit 5-6k RPM the tires would brake loose from the power.. Good luck trying to drive your car at 8k RPM all day long on the street, and the gas milage is no good either.
In the end it is all about having a useable powerband for the type of driving you are doing and the kind of car you are driving.