With 63dB attenuation, you are doing pretty well to get what you're getting.
This is one of the things that annoys me about the BT BRAS profiles. If these didn't restrict the flow of traffic then it could possibly squeeze another couple of hundred kbps out of your throughput rate. But unless you move to a LLU provider, this isn't going to happen.
Have you done everything on the
Low SNR page... including removing your ring wire from the master and extension sockets, and also using a filtered faceplate if that is appropriate for your circumstances? Even a 1-2dB increase in SNR may push you up enough to get you the 1250kbps profile if you feel it's worth it (you need to sync at 1440kbps or higher for that).
WORD OF WARNING!!Do not cause the line to resync too often when you are messing about. Or else BT's wonderful DLM
will raise your target SNR margin, up to 9, 12 or even at worst case 15, which would give you a slower speed than a fixed 512 connection on your line
By too often, I mean make sure you don't go over a couple of times within an hour, just to be safe. I don't know the exact threshold for triggering these DLM changes (I wish I did), but I do know that my target SNR margin is now 15dB, having started off at 6dB.
And you can't use the DMT tool for reducing your SNR margin on the Netgear DG834G (you can on the GT).
So try and improve it, but be careful you don't resync too many times.