The speed difference is not the story
415 fps against 405 is within the range that a heavier bolt or a tired string will move on its own. Nobody should choose between these two on that number, and the fact that they are so close makes the rest of the comparison unusually clean.
What separates them is the shot cycle. The Burner is louder than its class with noticeable hand shock; the Lethal is quiet for its price bracket and settles well in the hand.
Why quiet and smooth beat sharp and fast
A crossbow bolt takes long enough to arrive that a relaxed animal can take a step and an alert one can drop at the sound. A louder bow gives more to react to, and ten feet per second does not shorten the flight time enough to compensate.
Hand shock matters for a different reason: it trains a flinch. For a new shooter that is the single most expensive habit to acquire, and it costs far more accuracy than the Burner's speed advantage returns.
Where the Burner wins
It is compact when cocked, which is a real advantage in a blind or a tight stand where a wide bow catches on everything. It is also fast for the money, and if your shots genuinely run past 40 yards the flatter arc is useful. Both bows include a crank alongside the rope cocker, so cocking is not a differentiator here.
Which one to buy
Buy the Lethal 405HD unless you have a specific reason not to - it is the more pleasant bow to shoot and the more forgiving one to learn on, and it ranks higher with us for that reason. Buy the Burner 415 if space in your stand is tight or you want the sharper, faster bow and know what you are taking on. Read <a href="/reviews/killer-instinct-lethal-405hd/">Lethal 405HD</a> and <a href="/reviews/killer-instinct-burner-415/">Burner 415</a>.