It depends on what kind of application you are building. Create a representative test scenario, and start hammering away. Then you will know the definitive answer.
Besides your use case, it also depends on CPU, memory, front-side bus, operating system, cache settings, etcetera.
Seriously, just test your own scenario.
If you need some numbers (that actually may mean nothing in your scenario):
- Oracle Berkeley DB:
Performance Metrics and
Benchmarks - Performance Metrics
& Benchmarks:
Berkeley DB