As a control player, there are times where it takes a while to resolve the first game, and there are many times where I'm up a game. Are there any rulings against stonewalling the opponent and not taking any steps to end the game while playing at a reasonable pace? I feel prompted to ask this in light of Channel Fireball's article: Silvestri Says – It’s Time to Stamp Out Slow Play
No, there is no rule against playing so that the game as a whole progresses slowly, as long as you take all of your actions in a timely manner. The official tournament rules describe slow play (in section 5.5) as
Players must take their turns in a timely fashion regardless of the complexity of the play situation and adhere to time limits specified for the tournament. Players must maintain a pace to allow the match to be finished in the announced time limit. Stalling is not acceptable. Players may ask a judge to watch their game for slow play; such a request will be granted if feasible.
Note that this rule is primarily concerned with turn length and the pace of play. Stalling in this case means not taking any action or passing, such as by staring at your hand without actually playing anything on your turn.
If this seems a little ambiguous, the Competitive REL infraction procedure guide describes slow play more simply (in section 3.3) as
A player takes longer than is reasonably required to complete game actions... It is also slow play if a player continues to execute a loop without being able to provide an exact number of iterations and the expected resulting game state.
As long as you are completing game actions and turns in a timely manner, you won't break this rule.