first of all, use a RAM drive on both computers so that the storage medium is not the barried. I have set up a 1 GB RAMdrive on two computers(this was months ago agrueing the same fact as here so i'll use it 🙂 )
ethernet has an overhead in the range of 10-15%, depending on the switching hardware and efficiency of the NICs being used. With two Intel Gigabit cards I can transfer an ISO image of Suse8 accross the network @ 102MB/second sustained. the image is 785MB and transfers in just under 8 seconds. This is over Cu wire , not fiber.
next.
Cu wire can transfer gigabit just as well as fiber up to 80-100meters. the farther the cable run, the more crosstalk and weaker attenuation on the Cu wires where fiber has VERY LITTLE crosstalk and that is typically at strand ends where the optical connector leaks light at the point of connection. Fiber also has much better attenuation esspecially if the strands/cable is not bent and bent fiber causes more lost light.
Cu wire uses 8 wires/4 pairs to transmit 250Mb/s along each pair for a true gigabit connection.
Fiber uses two strands(typically), one tx, one rx(send/recieve, whatever you may want to call it.) fiber is really not "gigabit" but the light source is, if the light source were enhanced, fiber could handle much more. I would guess that single mode fiber could handle 100-200gigabit on a pair of strands if the light source were enhanced and the cable runs were 200meters or less.
also, their is multimode fiber which can send and recieve on the same strand, but this increases "crosstalk" and multimode fiber has less potential and less distance.
ANY arguements about Cu being slower is simply not true UNTIL error corrention on the data is significant and causes more re-send requests on the data and/or the cable lenght reaches the limits of Cu's conductivity and cause more data errors. remember, electrical signals travel at the speed of light, or VERY near it on Cu, Fiber offers no speed improvement.
in fact, wireless should technically be the quickest, but not the highest thoroughput. the shortest path between to places is a straight line.