Droid X
Apparently, there's a 6.21 SBF that is rootable:
Posted by m.ksy
The way to get root found! Install sbf from attached archive and then use the "DooMLoRD_v4_ROOT-zergRush-busybox-su" (also attached in the archive) to get root. All thanks for finding this method going to bukolov1 from Ukraine...