It's not like it can outspeed anything anyway. I would want to put Gyroball on it in the future though. Pin missile sounds good but it's kind of unreliable. I might just consider Toxic.
HP fire sounds a bit situational, but I think it's good.
0 SpA Forretress Hidden Power Fire vs. 252 HP / 0 SpD Forretress: 176-208 (49.7 - 58.7%) -- 67.2% chance to 2HKO after Leftovers recovery
Doesn't do much to Skarmory though.
0 SpA Forretress Hidden Power Fire vs. 252 HP / 4 SpD Skarmory: 78-92 (23.3 - 27.5%) -- possible 5HKO after Leftovers recovery