First of all can your motherboard take a 2800/3000?
If yes then i would say you would see an improvement. But how much of an improvement i really do not know.
The 2800/3000 are of the Barton cores so they have an extra 256KB of cache. This alone would improve things over the 2100. Also they run faster and the FSB is increased by 33MHz.
I would say you look here click here and other parts of the site for benchmarks.
But i would say you would see an improvemnt.