The D1X won't come close to having the ISO capability of the D90, but it has a unique image sensor that has both square and rectangular pixels, and with pro glass makes sweet, if small, images. I sold the last I had D1X about 8 months ago.
The D1X only has 5.3 effective MP, only 5 AF points, only a 2" rear LCD, and it can't handle CF cards larger than 2GB.
Even fresh, new, EN-4 batteries last for only a fraction of the time D90 batteries do, because the D1X is way less efficient at using power.
NOTE: 10MB output of 4,016 x 2,616 pixels with NEF (RAW) files can be obtained using optional "Nikon Capture 4" Software.
Not using the video on the D90 is OK, because being the first dSLR to also offer video, it sucks really bad compared to what is available on DSLR's today.
Here is what DP Review had to say back in June of 2001 when the D1X was the new Nikon top-of-the-line:
Nikon D1x Review: 1. Introduction: Digital Photography Review
I recommend getting the D90.