The only startup metric that matters
medium.com
medium.com
If you have stake in multiple companies I can understand why you would advice go for speed, as chances are big at least some will go in the right direction. And they may be ahead of more deliberately planned startups.
But as a founder with a limited amount of tries I'm not sure what I'd do....
https://medium.com/dusthq/the-pivots-are-constant-f9b191d954...
No one metric is the only one that matters. At each stage of a startup, a different metric will be the most important. Speed is a secondary metric, a multiplier of the primary, so it's always important but you can't just measure speed and be confident that all is well.