@ Unc,
You might just have made a typo ?
If so, there's quite a good chance your attenuation is more than 63.5 as that is the maximum allowed and therefore that Thompson modems usually report - unless O2 have adjusted their firmware.
I expect there are others, but the 2Wire is the only one I'm aware of that provides two attenuation readings on their diagnostics page, one specifically @ 300 Khz and the other I assume is the running average over many tones, similar to the usual calculation.
Perhaps somebody else might elaborate ?
Kind reagrds,
Walter