Your right, I really should go for 5 600 f/4s I would look cooler carrying those around, and that's what gear lust is all about, looking cooler than the next guy.
But realisticly I use 5 lenses for most everything (400 2.8, 70-200 2.8, 24-70, 16-35, 15 fish) That combo gets me through most assignments, but a thread asking photographers to theoreticaly pick their 5 favorites is silly. Every lens has a purpose, if you don't need it, don't buy it, if you do need it, go buy it.
Part of the fun of having photog. as a hobby (and not a job) is buying something totally cool that you don't need but would enjoy having. (Which is why I'm going to buy the 85...don't need it but would I think enjoy it very much.) When I think of all the canoes and bicycles and various and sundry things that get purchased and used once (at great expense) I don't feel bad about purchasing a lens, using it a lot and enjoying the results...truly, personally I don't care about looking cool...just enjoying my life in the scope (not overextending my bank account of course) that I'm able to.