how far can a PS3 or CPU be away from the wireless gateway/router and still have a good signal?

As stated there are many variables. I would say not much more than 150 - 200 feet at the absolute most. I know mine will work up to at least 140 ' because that is as far as my backyard goes and it still works.

It all depends on where you live -- how many walls are in-between the router and the device, what the walls are made of, and so on. The only way you will be able to find out is by physically testing the router with the device in person.

it depends on your router, space (walls,floor level), wind.