It is my understanding that as much as each individual kavalactone has a certain effect profile, the combination of all 6 is the key behind the effects. So isolating one or another doesn't translate to better results.
Ah, I knew about this at one point but forgot about it thereafter for some reason; good point. But I think (if my memory if serving me correctly) that the first three KLs in the chemotype have the most profound effects, so 2 & 5 being part of said first three would likely provide the majority of the effects. Also, I believe 2, 4, and 5 are the most understood KLs recreation-wise, so 1 (particularly), 3 (moderately so), and 6 to a lesser degree generally have somewhat subordinate (or at least, less-understood) effects for the recreational user.
Comparing different kava varieties and effects can be a bit subjective as it depends on personal preferences and individual body reactions. Some may find one type smoother while others might feel it's more potent. It’s often a bit of a trial and error to find the one that suits you best.
I've come to realize this, but I'm really trying to get something that's going to be anything-but-suble in its effects and, hopefully, blow me away... but I guess that may be wishful thinking.
However, talking about "body-oriented" effects, kava with a higher kavalactone content (the compounds 2 and 5 you mentioned) might provide stronger effects. But, this also might mean a rougher experience on your stomach or even more potent side effects, such as drowsiness.
I'm pretty sure 5 is more likely to have injurious effects, re: the potential for nausea, drowsiness & all of that. I think it's best if 5 is in fourth position or less, but it's also a sometimes unfairly maligned KL at the same time... that being said, I probably shouldn't have even mentioned 5, because FVK's Santa Cruz doesn't seem to be particularly high in it; I must have misread the COA for some reason.
2 & 6 (i.e., not 5) might work synergistically to confer more auspicious "heavier" effects in many of your noble kavas.