RGoodall: I have been looking for something like this for the last 2 weeks when my problem started, I am experiencing the exact same issues you are. I play warcraft 3 ( a 12 year old game) I have run this game on 2 computers at the same time on 64kps before when i went over my data cap.
As of 2 weeks ago between high congestion times as vodafone has been calling it my ping has been spiking massively and is very hard for me to show them except in everytest it lags then shows a massive drop the it shoots up high straight after ( never changes my ms though), Until the other night i ran one and i got screen shot to prove to vodafone what is happening.
In this speed test it showed my 501ms, They really struggled to explan this, I have talked to their faulting team for nearly 4 hours over the last few days and the customer serivice team for nearly 15 hours overs the last 2 weeks, They have run every test they can think of, Changed every setting they can think of......BUT STILL NOTHING.
The one thing i am waiting on now if a new modem which is on its way to me now and i hope that is the problem, Im also running the white HG556a modem.
I will post on here when i get the new modem and let you know if that is the issue.
( I have also been explained to me by some tech guy's, NOT FROM VODAFONE. That if vodafone has oversold its bandwidth then that could be causing the issue, Because it only happens in peak time's eg: 5.30-11.30pm everynight of the week and most of saturday and sunday. Im very sure that could be the problem, But fat chance of vodafone saying yes we oversold our bandwidth to make higher profits and your internet cannot be fixed because of this.)
Hope this helps
P.S - Tryed to upload the screen shot of 501ms, File size was to large and if i make it smaller it might not be viewable
Firstly the oversold bandwith theory doesn't make sense when you are already capped down to 64kbit bandwidth. If you go back over various threads of ISP's when they don't have enough bandwidth you tend to see drops in throughput at the high end. Additionally if you care to take a look at the independant reports on VF's throughput at peek times you may notice that VF rates consistently high. (www.truenet.co.nz) This would not be possible if VF did not have enough bandwidth.
I would suggest using some sort of network monitor software to look at what sort of useage your computers experiences when it has this problem. When you are limited to 64kbit it doesn't take much to cause a lag spike. I'm not even talking really obvious stuff like downloads in the background but something as subtle as a program sending a query to a server to see if an update is available.