Why difference in d-l speed between 2 routers?

I have 2 routers;
Old Buffalo WBMR-G125
New Zyxel P-660HW-v3.7

Having run multiple(@20) tests from various sites, including this one, I find the ping from the Buffalo always 10% lower than the Zyxel (40ms against 44ms so not much really), but the BIG difference is the download speed. The Buffalo always gets 5.40mb and the Zyxel 6.53mb - 20% better!

Big question is WHY - can anyone explain to me without TOO much network tech speak!

Thanks

Accuracy of termination impedance across the frequency range will be one factor. Any additional noise created by the modem will affect it too. Accuracy of measurement of signal and noise and feeding that back to the DSLAM is a third.

You will find differences between brands, models and to a lesser extent individual devices of the exact same type where component tolerances are not too tight.

What sync speeds and IP Profiles do you see with each of the routers?

Sorry, unsure about how to do advanvced stuff but here's data from diagnostics page of Zyxel router;

SAR Driver Counters Display:
inPkts = 0x00008064, inDiscards = 0x00000025
outPkts = 0x00006321, outDiscards = 0x00000071
inF4Pkts = 0x00000000, outF4Pkts = 0x00000000
inF5Pkts = 0x00000000, outF5Pkts = 0x00000001
txRate(Bps) = 0, rxRate(Bps) = 0

DSL Line Status:
noise margin upstream: 6 db
output power downstream: 0 db
attenuation upstream: 26 db
tone 0- 31: 00 00 00 46 8a bc cc cc cc cc cb bb aa 99 88 76
tone 32- 63: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 64- 95: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 96-127: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 160-191: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 192-223: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 224-255: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
noise margin downstream: 6 db
output power upstream: 12 db
attenuation downstream: 51 db
tone 0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 32- 63: 05 68 9a bc dd ed ee be ee ed ee ed ed dd de dd
tone 64- 95: ce ed de d0 dd ed dc dd dd bc dd bc dd cd dd cc
tone 96-127: dc cc cc bc cc cc cb 0c bb bb ab bc cc cc ca c0
tone 128-159: ab ba ba bb ab ab a9 99 69 9a aa ab a9 a8 75 74
tone 160-191: 00 26 8a 99 a9 aa 95 9a aa a9 9a aa aa 9a 09 80
tone 192-223: 04 75 75 00 05 77 88 88 76 87 88 78 78 67 75 42
tone 224-255: 02 56 66 67 75 65 66 54 30 00 00 00 14 43 00 42
tone 256-287: 03 44 41 34 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

DHCP: Server
IP Pool Starting Address: 192.168.1.33
Pool Size: 32

ZyNOS Firmware Version: V3.70(BJZ.10) | 06/01/2011

WAN Information:
DSL Mode: ADSL2+ Mode
IP Address: 85.210.xxx.xxx
IP Subnet Mask: 255.255.255.255
Default Gateway: N/A
VPI/VCI: 0/38

LAN Information:
IP Address: 192.168.1.1
IP Subnet Mask: 255.255.255.0

I can't see the sync speed in there - have you run the BT speedtest? The full output from that may be informative.