You may or may not be aware of project Sitara. One of the goals of project Sitara is to fix the handling of small packets.
I have achieved a milestone... using a hacked version of the nxge driver (diffs available on request), I've been able to get UDP forwarding rates as high as 1.3M packets per sec (unidirectional) across a single pair of nxge ports, using Sun's next sun4v processor. (That's number of packets forwarded...) This is very close to line rate for a 1G line. I'm hoping that future enhancements will get us to significantly more than that... maybe as much as 2-3 Mpps per port. Taken as an aggregate, I expect this class of hardware to be able to forward up to 8Mpps. (Some Sun internal numbers using a microkernel are much higher than that... but then you'd lose all the nice features that the Solaris TCP/IP stack has.)
By the way, its likely that these results are directly applicable to applications like Asterisk (VoIP), where small UDP packets are heavily used. Hopefully we'll have a putback of the necessary tweaks before too long.