Take this with some salt: I watched a video from Matt Dubber (spelling?) regarding the liners where he made a statement something like 34 grains, roughly, was the cutoff and beginning weight between the two liners Superior/Superior Heavy, and to try both. I've also read a few times where some have said the standard JSB 33.95s did better than the MKIIs. I've only shot the MKIIs in my STX and Superior liners. I can't say right now that there is a winner as I haven't focused on the MKIIs much in the short time I've had my Impact. I have been mainly working with slugs. I don't have a heavy yet to know what they are like.