Isn't 8 IP and 4 ERs even better? It is 4.50, as well.
Isn't 5.2 IP and 0-3 ERs better, too?
Why does it have to remain so arbitrary?
I realize that setting up new parameters will be arbitrary, as well, but it will be fairer and more accurate.
Something like this:
4 IP 0-1 ERs
5 IP 0-2 ERs
6 IP 0-3 ERs
8 IP 0-4 ERs
(One could argue 3 IP and 0 ER as being included, especially with today's trends, but I'd be fine with leaving that one out.)