It depends on your playstyle, and what ship you enjoy most.

I recommend getting KGV, and trying it out to see if you like it.

Depending on your support crew, I'd say go with the KGV. I haven't had much experiences
with the KGV and POW since I sort of really hated the two when I got there... From what I
understand, the 15" Mk3 N would be wise on the KGV, given the longer range and all. And
you'll want to learn or get more used to playing with range than rushing with the quads.

Save the dunk for when your engineers make it go 44knt and your spread is consistently
tight. Then you'll rape. ;)

You will need to buy it later to remodel in a pow, so why don't you buy it now ?
mark III N have more range than nelson 16", and the kgv is faster than the dunk (and you
can try a easy mode AW setup with 12" deck)

Dunk is a good ship, might wanna stick to it until level 82 when you can get the PoW? :P

After all
KGV = BB2
Dunk = BB2.5
PoW = BB3

Depends on you.

With mine when I was at-level with KGV, I had to use the Mark III Ns which have random
spread, if I may say it. Sometimes it groups pretty nicely and sometimes it's less than
shotgun spread.

Bearing in mind that I have non BVE gunners with less than the usual Vets, *86s front / 56
back*.

Keep in mind that Dunk also has one additional Support slot and *I think* that you will
lose that one when you use KGV. I don't have a Dunker so I can't say for certain.