Generally, the lighter the knife the harder you must throw. This is why most serious competing throwers will go with a heavier knife. The mass (weight) of a heavier knife will do most of the work of driving it in the target.
You must throw hard enough to stick the knife. Additional throwing speed (velocity) is purely an individual comfort issue. I am a bad example as I throw very hard... observed around 45 mph with a stopwatch at 35 feet. Sure this will stick a 14 inch 3/8 thick, 15 once knife 2-4 inches in a pine end grain target but I do not suggest this brutal type of throwing. How do you know if you are a light, medium or strong thrower? You will know a strong thrower when you see one throw. Just look for 20 foot bounces, targets knocked down and the guy using a tractor and chain to remove his knives from the target.
Most people have very good success with the heavier knives throwing around 30-35 mph.
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