A byproduct of your scrutiny is that I found that the scope of synchronization around the signature validation was wider than necessary, reduced it:

https://github.com/bitsofproof/supernode/commit/b750ef94a7f00756fd4fa2afe9a532caa4cf76e0

and it gives a real boost on my server.

This is nice, would you mind submitting a pull since copy from pastebin failed to patch for me?

Thanks a lot to all of you, this is exactly the feedback I expected and opened the source for !