After a few months of taking additional photos with the new Rebel T1i (500D) DSLR camera at various high speed settings, there really has not been any improvement in eliminating high end noise as compared to the early generation Canon Rebel XT. In fact, after some comparative study of detailed reviews carried out by professional camera webzines, the T1i fares slightly worse than the model its intended to replace, the Rebel XS (450D). And my test photos support this, too.
The good news is that noise reduction modes at ISO 1600 perform comparably with the 450D.
It is not a complete loss. Where the Rebel XT was an 8 mega-pixel camera, the T1i is 15!! Longer battery life, and more importantly no battery amp glow!! There is still much I would like to accomplish with DSLR astrophotography. In the near term, I am looking forward to eventually replacing the IR cut filter with a wider band version designed for deeper reds and extended UV.