Free: Contests & Raffles.
no set way to know without just testing...most bows your looking at about 2.5 to 3.0 fps/lb if memory serves me...so roughly 25 to 30 fps
one other thing, maxed out bows are generally more efficent than ones backed off some.so a 45-60 lb bow set on 60 lbs will generally be more efficent than a 55-70 lb bow set on 60 lbs....when you back off on weight, you can back off on arrow weight to get your speed back up, however, you'll not really gain that much in arrow arch because a light arrow slows down faster than a heavy one unless you improve dynamics of the arrow.... (same as bullets)
Maxed out is more accurate is what I have always been told. I recently bought a new bow and went with a 60# since I previously had a shoulder injury. I backed it down to 52 and started shooting. Working my way back up to 60. It is comfortable and I am not having the shoulder problems. Glad I went with the 60.