I just switched from a Stereovox HDXV to a Sonicwave glass Toslink, and the improvement was staggering. Overall, I've found the Sonicwave to have more air and real high-frequency detail, better detail throughout the audio band, better bass articulation, and is much quieter compared to my previous coax. The fact that I paid just $29 for it makes it that much sweeter.
This is just my opinion, but I've found that when it comes to digital cables, susceptibility to hum, EMF and RFI contamination is a bigger issue than bandwidth. The great advantage of optical cables is its total immunity to noise pickup and ground loops. While it's true that coax has greater bandwidth compared to Toslink, we're only dealing with SPDIF with a bandwidth of up to about 6Mhz (well within the limits of glass fiber), so I think that bandwidth is largely a non-issue provided that you use glass and not plastic optical fiber.
This is just my opinion, but I've found that when it comes to digital cables, susceptibility to hum, EMF and RFI contamination is a bigger issue than bandwidth. The great advantage of optical cables is its total immunity to noise pickup and ground loops. While it's true that coax has greater bandwidth compared to Toslink, we're only dealing with SPDIF with a bandwidth of up to about 6Mhz (well within the limits of glass fiber), so I think that bandwidth is largely a non-issue provided that you use glass and not plastic optical fiber.