If you’re doing 4 sets of 10 reps to failure with 25 lb dumbbells and can only hit 8 reps on later sets, stick with the 25s. That’s a sign you’re training hard enough to stimulate growth. You don’t need to hit all 10 reps every set—falling short in sets 3 and 4 is totally normal and still counts as progressive overload. Keep grinding with the same weight until you can hit 10 reps across all sets with good form, then bump up to 27.5s or 30s.