OK.
Kitty just to remind you pings are nothing at all to do with proxies they deal exclusively with web traffic not ICMP. Also if you are using Windows 2000 it tends to report sub-10ms pings as 10ms.
Oldham them Manchester? Network segmentation and best practise, spreading of load in Manchester throughout core rather than shoving everyone through the same (slightly lower spec) t2cams then to the higher spec t2cores, could be other reasons as well, distance of fibre run, arrangement of metro-net, etc.
I think some massive confusion is here people are forgetting that there are two distinct sets of cache in Manchester, Manchester Central (I think

) and Manchester Transit. One has 4 caches the other has 10, and it's perfectly possible that those on man
c-t2cores have transparent caching disabled while those on man
t-t2cores do not, and vice-versa.