Indeed the f4 version is sharper and has the 4 stop IS, whereas the 2.8 has what I read a 3-3.5 stop IS.
I bought it because I knew in the end, I'd kick myself for not buying it. Also, since I have alot of friends getting married in the next year or so, I figured it'd be great to have for the indoor, dimly lit settings. Worse comes to worse, I sell it. =T
Good taste Knuckledragger. Taking pictures of Grimlock. I was so disappointed that the next Masterpiece Transformer isn't Grimlock. I guess having Thundercracker is good since it completes the trio... but it's just so boring. Grimlock would have been an awesome addition to my collection.