A while ago YouTube put together a speed information page that you could use to check out your download speeds as well as compare to other isps in your area:
http://www.youtube.com/my_speed
I'm also on Time Warner, and my graph shows wild inconsistencies - sometimes it spikes up to much faster than others, sometimes it's way below the average speed, and it also shows that Time Warner is the slowest provider out of all of the NYC area ISPs.
I wish it was easier to switch to another provider out here.