Line rate doesn't imply small packets. But most userspace benchmarking uses 64B packets. That being said, the "imix" packet size, which is supposed to represent internet traffic, is around 500B.
There are numerous imix definitions floating around now, it really depends on who you ask. The more realistic ones define a pattern of different sized packets. And performance varies greatly depending on which imix flavour you use, which probably goes back to the earlier poster's 'dumpster fire' comment (although I don't know exactly what NPU generation they are referring to).