Firmware is never stable or static. All modern drives have some kind of "learning" function, and learning is not always good, or say positive.
Not having a real DW1655 drive (although my Philips 1660P1 and Lite-On branded DW1650 run nice @DW1655 firmware), BCHB seems to be a well balanced and not that media sensetive firmware.
And please, don't ask once again about what firmware is "best" because noone is able to give you a answer that suits your system, media or demands. You'll have to find it out by yourself.