It doesn't exactly scream out Plate 8 to me. I value my time fairly highly and I wouldn't even attempt to plate it. That's just me. If I was stubborn and had to try, Plate 8 might be my last stop. Believe it or not, an early printing from Plate 4 is not out of the question with this stamp.
As I've started to plate these 3c stamps, I've been able to do it in less than 5 minutes on a couple of them with near certainty, and others are very difficult that might require days to do it. Do those of you that plate stamps pick the ones with distinctive features and leave the indistinct ones alone?
I would keep trying the hard ones (sometimes after setting them aside for days or years) if they are in good shape. If they are missing a frame line or look old and worn, I wouldn't get around to trying again.
Your stamp for this thread doesn't quite match any of the 3 candidates you mentioned. (I'm looking at how the frame lines meet at the corners, distance to diamond blocks, the slight curves of the right frame line, the straightness of the left line...) Maybe one of them could match if inking differences and wear are considered, but it is time to try plate 4. If that doesn't work out, set it aside and take a fresh look later on.