I am wondering if anyone has some metrics or even a general guide as to when the use of vertex buffers outweighs immediate mode drawing for performance.

I have a mix of static and dynamic objects.  The dynamic objects vertices are calculated very often (30-60 time/sec), immediate mode is giving me the best performance (none of them will have huge vertex  counts).  Though this suprised me a bit, I figured the JNI overhead would mean buffers would always win, but they are about 5% slower (not sure why, it may be my video card).  

The static objects are the ones I am concerned about.  With very large objects buffers is winning hands down (say over 300k verts) with gains of 15-20 fps over immediate mode rendering.  But for smaller static objects (< 50k) they seem about the same.  (ARB buffers)

Basically, what I am asking is:  What would be a good number (in vertices) to use as a guidelne for using vertex buffers over immediate mode?

Thanks!