how far true are these figures?
256kb/s = 32KB/s - 2bit
512kb/s = 64KB/s
1024kb/s(1mb) = 128KB/s
1536kb/s(1.5mb) = 192KB/s
4096kb/s(4mb) = 512KB/s
8192kb/s(8mb) = 1024KB/s (1MB)
12,288kb/s(12mb) = 1536KB/s (1.5MB)
24,576kb/s(24mb) = 3072KB/s (3MB)
^note these are theoretical speeds, you will never reach the full theoretical speed as there is a 2bit overhead on PPPOE connections which makes the correct equation kb/s / 10, rather then kb/s / 8.