Benchmarking competitor download speeds

[Adam C]

Does anyone have any recommendations for tools or services to benchmark competitor download speeds?

Ideally something that can operate at scale to get a broader picture than individual testing.

[Drastic]

This one really helps you drill down on what's slowing down your page:
http://www.webpagetest.org/

It has a visual compare test (2nd tab) where you can insert multiple sites, but I've not used that.