For a usefull awnser it's good to know why you want what you want. I would say that it's pretty important on what account a character is, or will you just transfer them off?

Sidenote: For the RAF bonus to apply the linked characters both/all need to get exp from the mob. So you cannot boost with the 75 if you want to get raf. You'll need to boost on an other account. The lowlevel characters you're boosting should be the same level.