I think there is a big difference in optimum expansion and adequate expansion. Optimum expansion may be achieved at 2000+fps, but most bullets for modern rifles will still give adequate expansion at slower speeds, 1800 fps or less, in my opinion. Some, such as RN bullets designed for 30-30 speeds will give good expansion at much slower speeds.
Nosler shows some photos of their bullets at various impact speeds.
http://www.nosler.com/Bullets/Accubond.aspx. Only the Accubond shows a suggested minimum speed of 1900 fps.
While no speeds are suggsted for the Ballistic tip the photo they show at 1900 fps shows more expansion than the Accubond at 2000. I don't claim to be an expert and if wrong don't mind someone setting me right, but my take is that most standard bullets will most likely do the job as slow as 1800 fps. Maybe not as dramaically as if they impact faster, but still get the job done. The solid copper bullets probably work fine at more moderate ranges, but probably won't perform well if impact velocities are below 2000 fps.
