The attenuation reported by routers is typically based over the entire range of frequencies received and often calculated differently between models.
A router reporting a higher attenuation maybe good rather than bad, as if that router locks on to more weaker higher frequencies because noise rejection is better, then the average reported attenuation goes up, as the higher frequencies have higher attenuation.
BT's attenuation for faults and speed estimates, and the only one you can use to do a like for like comparison, is the attenuation at a specific frequencey of 300KHz, and the vast majority of routers will not show that by default.
The attenuation you see from routers isn't much use really unless you get the 300KHz value, you can use it as a guide, but when comparing routers, the best figure to look at to decide which one may be performing better is your sync rate and SNR margin together.
As you are maxed on ADSL 8Meg and so sync speeds are identical, then we can say that the ZyXEL is the better performer even with the higher line attenuation, because on the ZyXEL you have 9db of SNR margin, compared to only 7.5db on the TP-Link. The ZyXEL has been able to make use, quite likely, of some higher frequencies, which naturally have higher attenuation hence the increased figure where the router averages them all out. Because the ZyXEL has more to play with and more spare capacity, there is more signal to noise compared to the TP-Link.
Edited by PhilipD (Thu 16-Apr-15 14:42:45)