Do you mean lenses (i.e. plural)? If not, I'd be spending money on second (and possibly third) lenses. If so, have you really got the best lenses that you can buy? The box is so much less important than the glass IMO. $5k gets some absolute cracker lenses, especially in the used market!
I currently have one lens I have been working with for portraits which is a Darlot Paris. It is actually an old Magic Lamp lens, but I have removed the rear element, and flipped the lens over to get full 8x10 coverage. It is one of the best portrait lenses I have worked with for what I like to do. I also have some (no name) 12" lens that I have been using for landscape work. Iím in the process of researching the Nikkor-M 450 f/9 with Copal #3 for my landscape stuff. I would be very interested in any input you have on lenses as well. That was going to be another thread, but if you can help me here, that would be great.