Linux vs. BSD on EC2

After reading the prior thread about whether or not startups should use EC2 for hosting, I was left wondering what the leanest possible approach would be to hosting an OS image... and do we have a truly optimal image for this purpose yet?

From a strictly computational perspective, which OS platform is better suited for this? My guess is that this contest would be between Linux and BSD (Solaris has too fat an ass?). From what I understand, the BSDs are tightly engineered with the goals of performance and efficiency in mind (still has the best networking stack, or so I hear), whereas Linux may tend to be more hackish (I am not an authority here!). However, Linux's advantage could be its modularity, making it easier to shape it to specialized puposes (like cloud computing).

I've heard a lot of geeks say that although Linux makes for a better free desktop, a BSD would be their first choice as a server.

So, in the cloud computing landscape, who will perform better? A tight BSD image, or a tight Linux image? Which will be more efficient in terms of computational resources used?

BONUS QUESTION: Do you think virtualization services like EC2 will drive the creation of new *nix variants that are optimized for max price/performance on cloud services? If you know of any that exist now, please post links!