Anytime we are dealing with an automatic transmission especially one which is paired with a low ratio gearing and a heavy car such as the 300E, we need as much torque at as low rpm as possible to get the car moving.
Now, when you put a higher duration cam, such as the performance cams mentioned above, what you are actually always doing is taking some of the torque from low rpm and exchanging it for some more HP at higher rpm.
It is true that with today's more advanced computer simulation programs for cam design, we can minimize this tradeoff. Therefore today's cams can make up to some extend for the loss of torque by using higher lift and more carefully chosen lobe separation angles which in combination with more advanced exhaust systems can offset to some extend the loss of torque.
As a matter of fact, I happen to have such a computer program and if you can provide me with the specific data of the two cams (both the stock and the performance cam) I would be glad to run it for you and tell you how much torque you are going to sacrifice and how much more HP you are going to get in return.
Now, if you have a manual tranny, things are different because simply you can make up for the loss of low rpm torque by taking off the line at higher rpm or by downshifting accordingly and keeping the engine at the higher rpm. On the automatic tranny you do not have this option. Many people with automatic transmissions did the mistake of changing cams with the intention of making their cars quicker but soon realized the mistake.
There is another thing that may be of consideration and this is the fact that a higher duration cam will increase drastically the HC content of the exhaust and may not allow your car to pass smog. Of course this is of no concern for racing use, but I assume that you want your car to be driven in the street.