Next Step for Embedded Project

I'm comfortable with Arduino, but I need a Clock speed closer to 400MHZ rather than Atmel's 16MHZ.

Does anyone have any suggestions on the next best development hardware/software for embedded development on a chip nearer to 400Mhz?

I've looked at gumstix... Has anyone ever developed on these?
Is it straight forward? Easy?

BeagleBoard - BeagleBoard.org - hardware

My curiosity kills me... why do you need 400MHz?

My curiosity kills me... why do you need 400MHz?

Video?

My curiosity kills me... why do you need 400MHz?

Video?

Movement detection?
Color analysis?
Face recognition?

Audio?
High performance PID?
Robotics?
Cryptography?

Public health reform?
World hunger?
World peace?

Lefty

World peace?

;D
That would be great!

I was going to recommend SheevaPlug, put they have f...ed up the web site www.plugcomputer.org, so badly, at least for my Firefox/Linux, that I am not sure any more ...