If the 2800 Sempron is the 1.8ghz Part then it will pretty much equal the 3200+ Barton and maybe faster in a few. The 2500+ Barton will get beat in every single task against the Sempron. A Barton pretty much needs at least 400mhz to be on par with a 754 Sempron. And sometimes even 600mhz it seems. The Socket "A" cpu's seems to have stopped scaling well after the 2ghz mark. The 754/939 based cpu's scale much better. Partly do to the onboard memory controller. As the mhz of the cpu increases, so does the internal frequency of the memory controller. So, the latency decreases as the frequency increases.
Jason