i've never used the f4 but own the 2.8 version. I think it would depend on your shooting requirements. The 2.8 is pretty damn large and heavy. Sure it's a pancake lens compared to the 400 2.8 or something, but compared to a 70-200 or something it's in a whole other league. And that goes for the attention you're going to get as well when you whip it out, wanted or not. I have used my 70-200 instead as the attention this lens attracts can be problematic. I've honestly thought to myself, well if someone tries to rob me on my way to my car, i'll beat them silly with the 1dmk2 300mm2.8 combo, the guys at the forum will get a kick out of that, and i'm sure canon service can fix any damage. to the lens that is. The f4 is much lighter, less expensive, smaller, less attention getting, and focuses noticeably closer. That said if you NEED 2.8, and you can actually get this lens for 3k i guess you have your answer.