Having worked in 3D, including tools, it's my experience that features and productivity (=program is delivered on time) are the most important features :)
The code needs to be "fast enough"¹. Though this often means more attention to speed than in other kinds of software. To rephrase, speed is often necessary but not sufficient to make good tools.
¹ I try to avoid using "execution speed" and "performance" interchangeably, since a crashing, late or incorrect fast program is not a well performing program!
