Yes this is maybe a little bit weak, maybe not so much, it depends on the generation of your cpu. I guess the 2800 is its P-rating, not its real frequency ? My athlon-xp 2400+, which runs at 2GHz gets a perf index of 8-9 when I play the first 20 seconds of the default chopin waltz in the standalone. But a turion-64 @ 1.8Ghz, such as the one available in Muse Receptors gets a perf index of 14-15 and perform very with pianoteq, so frequency is not the only parameter.
If you have many applications running in background, or if you have cpu-throttling enabled (because you're running on battery for example), this may also have a negative impact on audio performances -- but the audio driver should not (except a very broken one maybe)