A single PC not capable of hitting 100% utilization of gigabit connection? are you high?
Gigabit ethernet = 125 mb/s
10 Gigabit ethernet = 1,250 mb/s
100 Gigabit ethernet = 12,500mb/s
With the price drops to 750 Gig and TB Hard disks making them affordable to most PC users, either one as a single drive is capable of hitting 120-130 sustained spreeds. But a pair of 500 gig SATA II disks in raid 0 is capable of hitting 180 mb/s write.
SCSI, especially the old ultra 320 interface (which happens to be in use for part of my media server) is best suited for high traffic file servers, where I/O performance counts.
I have a 16 x 74 gig 16 mb cache 15k rpm SCSI array, on a Compaq SMART array 5300 raid controller. Thanks to ebay the disks cost a grand total of $320 (yup, $20 apeice) the raid card another $18. A dual channel controller can do a total 640mb/s bandwidth across 32 drives. Though if i wanted to play up the cost, the disks cost $2500 apiece 3 or 4 years ago.
Sata performs best with large file transfers, like ISO images, or video files. Sata can do 300 mb/s per channel, With eSata and the port multipliers it's quite easy to make use of the full bandwidth even using $50 250gig 7200 rpm disks. My 4x500 gig 7200 rpm 16mb cache raid 10 array on a rocket raid 2220 controller (which cost all of $250 for the disks, another $25 ebay find for the raid card) can hit 250 mb/s sustained write.
Is it likely anyone could make use of 5000 mb/s bandwidth from a 40 gigabit connection? Not really, despite Sata 600 standard coming into use, but a small bussiness, or a large family of computer nerds could probably use a fair bit of the bandwidth. ( for example, i know of one household of 6 people, each with thier own desktop, laptop and as one of them is a programmer also has 4 Server's running 24/7, which requires 2 DSL modems and a 16 mb down/ 5mb up cable connection to run smoothly)
When you consider the fact that a 45 min television show in 1080p has a file size of 6-7 gigs, to stream in real time 8mb download speeds aren't worth a damn if more then one person wants to do anything online.