In networking, it is the norm to measure performance in packets per second, so with small packets. Unless you're performing DPI or encryption, routers only use the headers to take routing decisions, so whether the payload is 10 bytes or 1000 bytes does not matter: the processing cost will be identical. Only the hardware bandwidth will matter for large packets, though this is rarely the issue (I've hit DDR4 limits once using XDP, and fixed by adding another stick of memory);