I am experiencing extremely volatile performance from our TC cable-based Warpspeed connection and struggling to identify the cause.

Our internet experience is extremely variable, being quite good at times, but increasingly terrible - to the point of unusable - at others, and not in any apparently predictable way.

The bad news (from my point of view) is that using the VF/TC Speedtest on a wired PC connected via a Gigabit port to our router (TPLINK WDR3600), most of the time reports about nominal 100/10 performance. Even using the OOKLA Speedtest.net site, and the Chch Snap Internet server, reports satisfactory 30/10-type speeds. On some occasions though, the speed testing is noticeably 'bursty' (stop/start) and on a few trials it will either take a long time to connect or fail to connect at all, usually for the upload test

But who uses wired devices anyway? (Don't answer that.) 

Performance on a range of wireless devices, including phones and laptops, is appalling. Occasionally we'll get a purple patch of 20/7 - type performance. For the most part though, the download speeds fluctuate wildly between 0.4 and 10 and the upload speeds are commonly 0.05 if they work at all. Once again, usings speedtest.net suggests that performance is very bursty (i.e. short periods of good throughput and long intervals where nothing happens), and the uplink is particularly badly affected.

The obvious conclusion is that the problem is local wifi performance and with that in mind I'm posting a complementary query in the LAN forum (http://www.geekzone.co.nz/forums.asp?forumid=66&topicid=119355). However, using the common tools available to monitor wireless connections and performance I can't see an obvious problem, and some aspects of what we are experiencing sound very similar to more general TC-related network issues I am seeing discussed here.

I'd be grateful naturally for any suggestions of either things to check for, or methods or tools to determine what the heck's going on.

PS: This is my second attempt to post this. The first time the connection was so slow it wouldn't complete the post.