The 105mm f/1.4E is simply a super-fast, mid-tele; the kind of lenses for which I have an uncontrollable affinity; again, destined for portraiture and people shots.
For people, it's indeed a great lens, but actually it'll handle anything you throw at it. One of my favorite lenses ever.
The legendary 200mm f/2G was holy grail lens for me and I finally broke down and pulled the trigger on one off eBay last year. I bought it for shooting full-length fashion shots from a fair distance while still being able to drop the background out-of-focus.
It's indeed tempting
The 300PF for its superior light weight and the 300/2.8 for its speed. This is an either-or purchase decision.
I have been debating more or less similar 300mm-options recently.
I admit that for my use of lenses (walking a lot, and also pub/club/event-stuff) the 2.8 options seemed less than ideal due to the totally not subtle size
So I bought a 300PF this week for 900 euro incl. 1 year of warranty, and added a 1.7* TC for outdoors. I'll see how I get along with it, but the size&weight is really nice; I knew it was 755 grams but actually handling the lens was still a surprise; great for handheld operation all day long.
You could try it, and if the f/4 is too limiting, you can always sell it later and get the 2.8.