Bob Smith termination for Ethernet magnetics
Although it is better than nothing, the 75Ω resistors don't really match the common-mode impedance of nearly any cable in use. This value was used in Bob Smith's patent where he was using an unspecified cable measured in an unspecified way that happened to have ~145Ω of common-mode impedance across pairs. This value is commonly used everywhere, even though you can do better in most applications.

A value of 52.3Ω more closely matches CAT5 cable while 66Ω more closely matches CAT6 cable. For most applications an intermediate value between those two would work best. This eetimes article goes through the details, which I believe is the same as this Teltest Electronics Laboratory publication (PDF).