I recently purchased some Flat CAT6 Cable for a grand total of £4.64 for 15M from Ebay with the intention of passing it through some double glazed window seals. When it arrived I was slightly taken aback at just how thin the cable was, around 6mm wide and 1.5mm thick. Great for squeezing through a tight window seal, but perhaps not so great for pushing packets.
2p for scale
To see if my scepticism was warranted I ran some iperf tests, and at 925 Mb/s I can't fault it-