I2P downloading at 30-40 kBps is perfectly possible. It might not be very fast compared to non-anonymous networking, but still, that's quite okay. When downloading large files, people just leave their downloads on for a while anyway.
Visiting I2P websites (known as eepsites) is also quite fast.
The same goes for visiting websites through Tor: the latency is high, but doable (depending on how much latency you're willing to tolerate :p).
I can't comment on Freenet, as I haven't really used it yet.
And no, I'm not on some super-connection, just cable.