We'd be fucked if monkeys were as smart as us. A chimp would rip a UFC fighter's arm off and beat him with it as he bled out.
But a monkey as smart as us wouldn't be a monkey. Our intelligence is predicated on several physical limitations that I know of, and I'm not a Scientist.
One being that apes (chimps are apes technically, not monkeys) don't have as much gray matter in their spinal cord. Human spinal cord actually has a mild cognitive function, but it's slower. Neurons are 'gray' when they don't have a myelin sheath, which speeds up transmission of signals.
So chimpanzees and gorillas appear to be amazingly dexterous, but not compared to us. The human ability to control our fingers for example is absolutely stunning, because there is some thinking going on outside the brain right down to the muscle.
A chimp, otoh, is amazingly strong. They can activate MUCH more of their muscle fiber because the myelin sheath carries a much stronger, though less finely-tuned, signal to the extremities.
So you are either hyper-dexterous and intelligent, but not as strong, or you are as strong as a chimp, but playing Chopin Op. 53 is out of the question no matter how smart your brain is.
That's just one thing I learned about in low-level bio courses in college. There are many more. Metabolic as well.
We could make very smart apes, but not Planet of the Apes smart, or they wouldn't be apes. They'd be monstrous, and not in a cool or scary way, but I guess we will find out soon when a Chinese scientist defects and lets us know.