Wireless is a lot more vulnerable than wired LAN. Almost everything technical in our lives today sends out EM radiation, which can massively disturb your wireless experience. So it is absolutely possible, depends on the strength and quality of the signal received.
Like I said, some ISPs throttle speeds. Further 'party poopers' are antivirus- and malware scanners, as well as firewalls and security programs. They inspect traffic for bad packets. And packet inspection is time consuming...
Disk fragmentation is not so likely, 200K per second should be reached by any HDD even under worst conditions.
