The theoretical capacity of fiber is somewhere north of 1 petabit per second. However, that requires some extremely expensive gear. A more practical limit today is 100Gb/s. That only requires some pretty expensive gear.
Cable Internet is a function of the number of channels that you’re willing to devote to access. It’s high, but always going to be less than fiber, as the base bandwidth of the cable is lower.
DSL is far, far lower.
The real question, I think is about which access provider is going to win. That’s much more of a business issue. It’s very clear that DSL in the long run will lose, and that as things scale up, cable itself, as a shared medium, will also lose. However in the near and medium term, the cost of fiber per home is still higher, making cable more economical, for now.