Question:

Which is more important for hunting whitetail deer, speed or kinetic energy?

Answer:

A good question, but the simple answer is - neither!

The most important thing when hunting whitetail deer is accuracy!  Whitetails, our most popular game animal, is not really hard to take with fairly lite archery equipment.  Any compound bow of 40 pounds is more than capable of a double lung shot.  It doesn't take much kinetic energy to push that arrow through a whitetail.

Speed is most important when trying to judge unknown distances.  The faster the arrow, the flatter it will shoot, and the greater margin of error you will have in your yardage judgment.   Speed is really important to competition 3-D shooters for this very reason. 

For hunting, especially whitetail, I want accuracy.  Many guys will try to get the fastest bow they can.  That is fine, but when you overpower your bow, your accuracy declines.  My advice to you is shoot a bow that you can comfortably shoot and practice until you can hit where you aim every time.

I have also posted your question in the forum section.