Do you know of any pretty well known graph parameters which are equal for all small graphs (for $|G|$ small)? That is, there exist two parameters $a(G)$ and $b(G)$ such that $a(G) = b(G)$ for all graphs with $|G|$ at most $k$, where I will require $k$ to be at least 4 to make things somewhat interesting.
I added "pretty well known" to eliminate defining a new graph parameter trivially to make it work, e.g., let $a(G) = \chi(G)$ for all graphs with $|G| \leq 1000$ and let $a(G) = \pi$ for all graphs with $|G| > 1000$.
The more well known the parameters, and the larger the value of $k$, the better the example!