Upload & Sell: Off
I say it really depends on what you are shooting, and how much you want to push the iso. I had the f4, and it was a brilliant lens; I really loved it. And for most any outdoor application with decent lighting is was just fine. Then I tried to shoot volleyball in this dingy private gym. F4 just couldn't cut it. I was at iso 3200 and getting shutter speeds in the 1/200-320 range. After that I sold the f4 to help fund a f2.8 and have not looked back.
Sure, you can fix the noise in post, blah blah. I needed to have decent stuff straight out of camera, and that one stop made the difference between what I considered usable or not usable.
So, bottom line, if you don't NEED 2.8, then the f4 is a wonderful lens that you will LOVE!