No, wireless G and N speeds are not necessarily overkill. G speeds are 54Mbps, and N speeds are 300Mbps. Hard drives can handle up to 3Gbps (SATA connection).
If using internally (between two computers on the same network), then the computers can utilize the bandwidth. In fact, most computers today use Gigabit (1000 Mbps), rather than the old 100 Mbps.
If using externally (through the internet, for example), then it's overkill. Because your internet connection is probably something like 7 Mbps download, and 384 kbps (0.3 Mbps) upload. So having the extra bandwidth wont matter then.
Basically, your computer and hard drive can handle whatever network connection you give it, easily.
no, acually wireless g is kinda slow. I would go with Wireless N thats what i have and i love it. The faster the better!