I also did quite a bit of benchmarking, and never saw any quadratic behaviour [0]. However, there is a floor for RSS and and elapsed time, but you would need to test assets less than ~1MB to see it. For assets over a limited range, the graph might look quadratic, but if you cover a large enough range you will see there are two regimes of behaviour.

[0]: http://stonecode.ca/posts/binc_benchmarks/