Measuring visitors connect speed

[shocker]

I want to measure a visitors connection speed to determine which content to display.
This may not be doable in javascript, but can someone tell me or direct me to the technique (code, example) to do this?

[Medyman]

A quick Google search displayed this: http://www.gambitdesign.com/bandwidthmeter/
It's in PHP.

But I think the optimal way for this would be to let your users choose which version of your site they want to see instead of assuming their preferences.

If a user wants has a low speed connection but doesn't mind waiting for content to load, why should he/she not be allowed to? Alternately, if someone with a high speed connection wants to see the less bandwidth dependant content, why should he/she not be allowed to?