Try *type* of cable instead ?
Is the cable cat5 ? cat5e ? or cat6 ?
I laid around 600m of cat5e in my house which is good enough for around 300mbs and I get wonderful pings between equipment pity I didnt lay cat6

silly me nevermind next house maybe...
with cat5e here are my pings :
pinging the cable modem
(bedroom 2 -> node 0 (10m) -> bedroom 1 (10m) -> router -> back to node 0 and the cablemodem (10m dowstairs) = around at least 30m of cable
root gw:~> ping 192.168.100.1
PING 192.168.100.1 (192.168.100.1) from 10.0.0.10 : 56(84) bytes of data.
64 bytes from 192.168.100.1: icmp_seq=0 ttl=63 time=2.782 msec
64 bytes from 192.168.100.1: icmp_seq=1 ttl=63 time=2.688 msec
64 bytes from 192.168.100.1: icmp_seq=2 ttl=63 time=2.688 msec
64 bytes from 192.168.100.1: icmp_seq=3 ttl=63 time=2.701 msec
64 bytes from 192.168.100.1: icmp_seq=4 ttl=63 time=2.611 msec
64 bytes from 192.168.100.1: icmp_seq=5 ttl=63 time=2.630 msec
64 bytes from 192.168.100.1: icmp_seq=6 ttl=63 time=2.616 msec
64 bytes from 192.168.100.1: icmp_seq=7 ttl=63 time=2.604 msec
Pinging the router
(bedroom 2 -> node 0 (10m) -> bedroom 1 (10m) -> router = around at least 20m of cable
sweet pings
root gw:~> ping 10.0.0.1
PING 10.0.0.1 (10.0.0.1) from 10.0.0.10 : 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_seq=0 ttl=64 time=261 usec
64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=199 usec
64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=191 usec
64 bytes from 10.0.0.1: icmp_seq=3 ttl=64 time=200 usec
Pinging the cable modem directly from the router around 10m of cable
These pings look high but they have always been that way no matter what length of cable (cr8ppy cable modem me thinks)
root myhome:~> ping 192.168.100.1
PING 192.168.100.1 (192.168.100.1): 56 octets data
64 octets from 192.168.100.1: icmp_seq=0 ttl=64 time=2.8 ms
64 octets from 192.168.100.1: icmp_seq=1 ttl=64 time=2.6 ms
64 octets from 192.168.100.1: icmp_seq=2 ttl=64 time=2.6 ms
64 octets from 192.168.100.1: icmp_seq=3 ttl=64 time=2.6 ms
64 octets from 192.168.100.1: icmp_seq=4 ttl=64 time=2.6 ms
64 octets from 192.168.100.1: icmp_seq=5 ttl=64 time=2.6 ms