I think we have to define what we mean by "pace".
I concur that being a running team isn't necessarily going to solve much and may just make us an exciting team to watch lose games. The problem historically for running teams is that while they can sometimes do well in the regular season, as a rule, they tend to get shut down in the playoffs.
Last year, some of the teams ranked high in Pace (possessions per game) were teams like Philly, LA, Denver, Minnesota. The Spurs were in the upper end of Pace in the regular season, with a 95.0 Pace rating -- but it's important to note that they were able to go much slower in the playoffs. In their three playoff series, they played at a Pace ratings of 91.2, 93.4 and 87.4 (in the final).
The playoffs tend to have better transition defenses and they do a better job of forcing you to play in the half court. So teams that win in the playoffs tend to be those that can execute well in the half court.
Historically, the Celtics franchise has done better with teams that rank low in the league Pace rankings. Only a couple of Celtic teams have made it to the conference finals when ranked highly in Pace. Most Celtic teams that have made it to the ECF or NBA Finals have been ranked near the bottom in pace.
The overall "Pace" stat by itself is not necessarily very revealing, though. It also incorporates the effect of the opponent's possessions. And frankly, making your opponent take forever to score (or preferably, to get a late shot off that misses) is a _good_ thing. Ideally, you want your opponent to score slowly while you yourself score quickly. These two things are in opposition in the Pace stat.
Steven's Butler teams tended to use up a lot of clock on both ends of the court. They were good at slowing down other teams and then they would take a lot of time methodically creating a good shot on offense. But while the result was a slow "Pace" number, the activity level was often pretty frenetic.
I think what he wants by 'fast pace' isn't necessarily about having a running team or transition game (though obviously those are great whenever you can get them). I think what he wants is for the team to work the motion offense at a higher pace than last year. Last year, the team would sometimes take forever to get into their set and get started. And sometimes it looked like the guys were tentative and moving in glue (especially if you compare them by watching the Spurs run a similar offense). I think Stevens wants his players in motion early and to keep moving -- those are consistent with the tenets of the motion offense.
One of those tenets is to never pass to a player who isn't in motion (because those tend to be the highest chance of turnover). If you see the ball sticking in the motion offense, it is likely because other players aren't moving.
