4 as in total points after hatch or 4 in sense?
Well, if you're bossing, all you need is skunk if you kill fine. But if you want the extra oomph in your damage, go for any guardian with at least a 4 in sense for SB.
If you meant 4 in sense, then those people are lazy/only want to do the bare minimum for SB. I honestly would go for the full 6 for the extra slots for Luckyfist and sticky icky if it permits it.
Aim for a 3362 Ifron or Spinel if you only care about bossing & CT. Aim for a 6143 Sephirens if you feel like you'll harkon once in a while and boss often.