performance - Load testing nginx inside AWS

I'm trying to load test nginx running on AWS. I need to
try to optimise it to handle 1Gbps of inbound traffic.

Currently I've got it to peak at 85Mbit/s by
running nginx on an m1.large with 4 other machines hitting it by using ab with -i (for
head requests) -k (keepalives) -r (ignore failed requests) -n 500000 -c
20000.

I'm struggling to generate more than 85
Mbit/s traffic from 4 machines, yet when I do scp a large file I get nearly 0.25Gbit/s
of traffic going over the
network.

Are there any tools or
approaches that I could use to load test nginx that might generate more load? I'm only
interested in inbound traffic, so perhaps a DoS tool could help if it chucks away
responses?

I'm hitting a very small (40 byte)
static asset, and have peaked at handling 50K concurrent connections and getting 25k
reqs/s when just using a single load generator machine.