I use 2-8 and always go for dead weight of 2-8 and if pick is good, it is a bonus, if pickup is bad, I try to reduce weight little more by removing stickers, toe guard, using lighter grip etc. I found that good pickup for heavier bats only matters/useful for straight bat shots, but for horizontal bat shots, dead weight always comes into play no matter how good the pickup is (This last statement should be a new post in itself to discuss further I think). I would think the suggestion should always be "use the heaviest you can" and not "use lightest you can" as if you can wield a heavier bat, you will definitely get more output from your shots, all else being same. Also, use heaviest bat you can only means the heaviest bat with which you can play all shots freely for the bowling speeds you play in your league. Doesn't mean just what you can lift and do a few shadow practice shots and feel ok..
Lastly why do i use 2-8? - my thin arms cant wield anything more than that.. if i had strong arms, i would definitely use the likes of GN 50+ at 2-15..