I wouldn't worry about the bearings. There may be a measureable difference, but that doesn't translate into a humanly audible difference. Bearings will only affect idle noise, which for all current IDE drives is basically dead silent. Once you put it in a case with fans, you really need a silent environment and some great hearing to hear an IDE drive spinning. It's generally accepted that it takes a difference of 3dB to make a noticeable difference in volume, but if the louder one is already inaudible, making it quieter doesn't make any difference.
SR said the following of the regular D740X:
"idle noise should be undetectable in all but the quietest systems"
If the 2 drives cost the same, by all means go for the FB version, but don't spend extra money on it thinking you will notice the difference.