[spitfire]

Michael Abrash talked about this in his black book of graphics programming.

WHen he was writing quake, they could trade off between lighting fast graphics (40fps+, on a 486) 99% of the time with the occasional horrible slowdown to less than 5fps. vs a steady frame rate that never changed much, but wasn't terribly fast.

Turns out people notice the occasional horrible lag much more than when things perform uniformly.

When tuning a performance critical service, focus on the outliers.

[jamesaguilar]

I think you should not ignore either. By default, think about 99%ile and 50%ile when tuning and optimizing. Depending on the context (e.g. games), even 99%ile might not be enough, or you might want to think about 99%ile of what? Frames? Scenes? Seconds of gameplay?

Also, back to the topic of the article at hand, I hope that their "T" is not really two seconds. That is already way too slow for most web purposes.