Predictability is a key feature

You can run a rally car on ice. You can travel under water. You can create a fast program based on slow components.

This is all due to predictability. While racing on ice you know more or less what friction you will get and what it will take to change direction. You will know how far you need to see ahead to be able to stay on track. If that criteria is met you can go as fast as possible.

On the oter hand, if you are racing on a mixed surface, you have to go slower. While you have traction you have to drive with a big margin to be able to control your skid if you suddently loose traction. While you lack traction you have to drive slower because if you skid around the corners and reach a high friction area you will end up in the ditch. Given the choice I would definately choose the high predictablity over max traction.

If you know all the parameters of a software project up front you are pretty safe. If you know all the parameters up front, you will also be the first in history to do so. Are you so sure of your requiremetns that you can choose components that fulfill your requirements but are not flexible enought to handle requirement changes? Are you so sure of your performance demands that you  can choose components that perform well but don't scale if your demands change?

Flexibility is often a an underrated feature. Its hard to put in sales brochures. Its hard to tell customers that the extra cost is to support their requirements in the future that they are not aware of yet. Often it has to do with how mature an IT project organisation you are dealing with. The more mature it is, the greater the chance of it expecting changes in the future and the more flexibility it wants from its IT systems. My experience is that these changes will amerge before the end of the project and the flexibility will end up saving them money before the project has ended.