Most of you will be able to temporarily suspend disbelief and accept superfast computers, brain implants, and designer drugs. You just have to assume that someone will develop them between now and sometime in the next century. However there are some fundamental rules that Egan deliberately bends. Quarantine's basis is that an inpenetrable bubble has been placed around the solar system thereby cutting us off from the rest of the galaxy. But unfortunately I know quite a few sf readers who would be appalled at the liberties he takes with the universe.
Permutation City is closer to home because it is mostly about computer software.
The Copies can be exactly the same as real people as they have fake software-simulated bodies and Virtual Reality piped directly into their senses. There are two things to warn you about. The first is that Egan seems to agree with the proponents of Strong AI who say that if a piece of computer software behaves intelligently then it is intelligent. A major plot device is the philosophical consideration of whether or not a copy is the same person as the source human. In the book the law says not, but most of the copies feel like they are normal sentient beings - but without flesh and blood bodies.