If there are only 2 PC's or devices attached to a hub its as fast as a switch. If more than 2 are attached to a hub, they all have to share the available bandwidth. If use is light, there is no performance difference. If use is heavy (busy office network, servers & internet access & printing, etc.) performance can go down fast.
I don't know of any real benchmarks because the hub vs switch debate was pretty well decided before everything became popular on the internet but you can try a google search - maybe someone's paper was published.
If there are more than 2 devices connected to the switch/hub you will probably notice a difference between a hub and a switch when you do file transfers. I dont know of any place you could even buy a hub right now and even so, switches are so cheap why not get one?
A hub is basically a multiport repeater. As in, it is a layer 1 (physical layer of the OSI model) device only. Which means that a hub doesn't care what port is sends traffic out of except the originating port. A hub forwards traffic regardless of destination MAC to ALL ports except the originating port. A hub is one large collision domain (more collision domains = better) as well as a broadcast domain. This would cause excess traffic on even a 5+ computer LAN IMHO.
A switch is a multiport bridge in that it is layer 2 (data link layer of the OSI model). A basic layer 2 switch keeps track of the MAC addresses of the NIC's that are connected to the switch ports and will only forward traffic to the appropriate port. A switch can support full duplex communications also. A switch creates more collision domains (which is good) but still is a broadcast domain since it will forward a broadcast frame (MAC address with all F's) to every port on the switch.
In short, go with a switch instead of a hub. The above replies are accurate - two PC's on a hub is no difference from a switch. Anymore and your LAN bandwidth will be wasted from forwarded frames that most will just be discarded by the host PC's NIC.