No argument from me that if you need f/2.8 or want to use teleconverters then the f/2.8 version is a better choice. The size/weight advantage of the f/4 shouldn't be underestimated though - it really makes a huge difference. It's the reason I bought the f/4 and only rent/borrow the f/2.8 on occasion. I really have to think about whether I want to lug the f/2.8 whereas I'll grab the f/4 without a second thought.
In any case it shows that the OP should be happy with whichever lens they end up choosing.