Left 4 dead and COD games can run pretty good on most pc's so i dont think u should use that as a bench mark. Same thing with world of warcraft, u should atleast be able to run that game at full settings(ultra) because its not very taxing at all.
In addition to this being a new game, so im assuming it requires better specs than wow does, as well as it being more action orientated, lag is the last thing u want as the delay will make things worse. And from what u said(wanting to run it on medium /high settings) i would recommend a few upgrades.
That being said i have not played the game or the beta :( so im just giving u my opinion in general. I have a better spec pc than u and i myself woudnt risk getting it on pc :)