If you use PABowhntr's calculations you will come up with a speed as if you were shooting through a crono.

Now I believe if you use davidmill's calculation's you will get the downrange speed which will be a lower number.

Your bow will be shooting the same speed but is quicker coming off the bow and slows as friction slows it down range.

For setting the speed on my Savage QCRanger I need to have the more exact down range speed . which is about 30 fps slower than the crono.
So if you want to brag about your speed use PA's numbers , if you want reality use David's