Was thinking about this the other day... and was curious what others thought about these two ships.
Now, first, I've not done a grind through either of these since like 2007... but that being said I have -used- them since that time. Many years ago, KGV was one of my favorite BB's... one that I kept because it was fun. Then, I suppose around 2009, A BB patch came out that made KGV.. in my eyes.. completely useless.
Back in the day, it was slower than POW, had the same guns as QE, BUT it could out-armor any of them. In fact, It was about the only UK ship other than nelly (at that time, no longer) and L1+ that COULD functionally armor.
Today, that is not the case. Now, I feel you are better off keeping the small and nimble QE with 4 guns than upgrading to the much weaker KGV with 1/4 less fire power. I suppose the only reason you should change from QE to KGV is to remod it to POW... Otherwise I would avoid the KGV as it is WAY too weak in modern NF after new nations and BB6's and such. It was great, got ubernerfed HARD, and now has no use in NF.