Bear in mind also that, regardless of ADSL performance, the overall stability of the router is important.
My only experience of the '585 was the 585V7. It did perform very well in terms of connection speed and noise tolerance, but the darned thing had a habit of locking up solid, requiring a power-cycle reboot as often as several times a day. That's not just an inconvenience as, if it happens often enough, BT's DLM can interpret it line-instability, and increase your target margin (reduce your speed) to compensate.
I'm now on my second netgear (DG834GT) and have found them to be very reasonable in adsl performance as well as stable in other respects, although the first one died prematurely (aged just over a year) owing to poor quality electrolytic capacitors, several of which were bulging and fit to burst when I looked inside at the autopsy. Hopefully (?), later models will have better quality components.
- 7LM