Considering there's a semi-contiguous allocation in the kernel I bet you'd find some interesting bugs that way. I don't think very many people mess with the pipe sizes other than to tune to a multiple of the input/output block size for the application. And if you're trying to maximize throughput you're likely to reach your optimum block count long before you start blowing out buffers.

Actually, come to think of it named pipes would be another good place to fuzz.