I just got a BB for my mark iv and i love it you feel your notes sustain for days i will say i love my mark iv tone as is... i only use the BB for slow leads and flowy stuff but for sticcato stuff and rythm tones i use just the IV.
Heres ones i posted awhile back that helped me out alot.
http://forum.grailtone.com/viewtopic.php?f=13&t=31324