"Every hour" would sound strange. Also, you don't need "at" if you use the verb "reach" in this sentence. "A cheetah can reach a speed of over 110 kilometers per hour." or "A cheetah can run at a speed of over 110 kilometers per hour." Good luck!

You would only use EVERY HOUR for something that really does happen every hour. Example, the Amazon river empties 27,000,000,000 gallons of water into the ocean every hour. A cheetah does not run for an entire hour or day. PER HOUR is the common usage for speed. BTW, I just made up the numbers for the amazon, so don't quote me on that.

1) No, don't use "every hour." "Per hour" is a standard way to express speed. 2) Yes, as Ian noted, you can say "run at a speed of" or "reach a speed of." Either would be fine. There is a tiny difference of meaning between them. "A cheetah can run at a speed of over 110 kilometers per hour" simply says that you could measure a cheetah's speed and get that number. It says nothing about how long it can maintain that speed. "A cheetah can reach a speed..." suggests that the cheetah is accelerating, putting on a burst of speed, running faster and faster. If you measure the speed, you might see readings of 80, 90, 100, 110, 113 kph. It starts at zero. It passes the speeds of 80, 90, 100, and 110 and finally "reaches" 113 kph. It suggests it is difficult for the cheetah to get to that speed. Perhaps it can't do it for very long.