There is no "perfect" rep range. Progress can happen with multiple workouts/phases. It all depends on your goals.
Every rep range serves a purpose. So don't always be stuck on 8-10, 12-15 or 5x5, or one specific rep range you feel is "perfect." No matter how perfect you think it is, give it a rest from time to time. Whether its perfect because it gives you endurance, muscle gains or strength….it's good to break away every now and then.
How about trying higher reps after a long stretch ( weeks ) of low/heavy reps. OR- dropping reps and really trying to challenge yourself in that 5-8 rep range with heavier stuff if you've been hitting the high reps.
You never know if you never venture out from that "perfect" routine. Maybe after a long phase of high reps/circuits going BEASTMODE ( lol, pick up some HEAVY stuff ) could be exactly what you need to kick that stalled progress back in gear.
Add Variation to your routine more often! #fithappens