Wow. That load order is a little long. I would say instability with your load order is to be expected. I have a few questions about your problem:
Are you also running an ENB? (if so which one?)
Does your framerate go back to normal if you quit game and relaunch New Vegas?
What is your CPU clocked at?
Sometimes when I run an ENB, my framerate will tank really hard for no reason. However, if I look at the sky, the floor, or move around a bit my frame rate will jump back to solid 60.
If your fps goes back to normal after restarting your game, then this problem is normal. I've just never seen it to the extent that your are getting, and it may be due to your load order. Maybe someone else can chime in with some other ideas. These are just some problems that I've had over the years that sound similar to yours.