I have a 50D and find the so called reviews claiming poor high ISO performance to be a giant load of crap. Not only was I very happy with the quality of such shots early on with this camera, I have been extremely impressed with the results after updating the firmware to the recent release. A friend of mine has two 5D MKIIs and thinks the 50D puts out the same level of low noise performance, after updating the firmware.
I can see no possible scenario where the T1i would be a better choice unless you have really small hands, or just want the video recording feature it offers.
Ken