Telstra Clear already do this with their tempest service, if you purchase a 256k connection, check your router status and you'll see you are connected a 288k. They at least give 32k leaway.
Just checked a clients tempest connection and the Nokia router reports: Downstream Upstream Current Rate : 8000 Kbps 800 Kbps Maximum Rate : 9523 Kbps 941 Kbps And the latency is somewhat better than what we used to get from the jetstream link: traceroute to xtra.co.nz (202.27.184.102), 30 hops max, 38 byte packets 1 a.a.a.a (a.a.a.a) 0.926 ms 0.864 ms 0.922 ms 2 b.b.b.b (b.b.b.b) 8.465 ms 8.123 ms 12.425 ms 3 cs2-e4-7-acld.auckland.clix.net.nz (203.97.9.98) 8.771 ms 9.305 ms 9.286 ms 4 g1-0-927.u11.tspn.telstraclear.net (218.101.61.6) 11.422 ms 10.660 ms 10.282 ms 5 xtra.ape.net.nz (192.203.154.60) 14.338 ms 10.610 ms 10.278 ms 6 v512.XTRAK2-B1.xtra.co.nz (202.27.176.226) 11.048 ms 10.160 ms 10.023 ms -- Stephen