For a cigarette blend, I would suggest starting with 5% Perique, then work up from there in small increments (like 5% per adjustment), in order to find a taste and potency you like. Cigarette smokers usually expect a relatively acidic smoke.
In pipe blending, the assumption is that the actively combusting tobacco (the cherry) is much greater than with a cigarette. My usual goal with a pipe blend that includes flue-cured as well as Perique is to eliminate tongue bite. For Lemon Virginia, that balance point is roughly 5 parts Lemon to 3 parts Perique. With redder flue-cured, the proportion of Perique decreases somewhat.