Do large frogs such as the king daddy have much for improvement on the size of fish, or do they just make it harder to set the hook?  

It really comes down to matching the size of the other frogs the fish are eating.  I've fished them and have not caught bigger bass, you will be surprised how small fish still eat it. 

I've never seen a bass, or any fish for that matter, try to eat a very large frog, especially a bullfrog that I think those a mainly meant to look like. No doubt a big fish would eat one if you threw it enough, but I don't think your catch of big fish would improve any over a regular sized frog. 

I had a 13" bass take on a 12" culprit worm. He bit the head. Does size really matter? I still say big baits = big fish. I purchased the largest bull frog that bog baits offers. The jury is still out.

have not used this but would think it be have potentially some better drawing power if you are fishing vast expanses of weed/slop areas. Think you would be better off throwing at targets/cover with the 65 size. 

I have fished the 316 no bull frog for about 5-6 years and big frogs do produce big fish...but so do regular sized frogs.  Its just really fun to throw the no bull frog to be honest

I pretty much have narrowed down my frogging to the mid-size frogs. Using LiveTarget HB's for example the 55T size are ideal for me. 

I caught a 13oz bass on the king daddy...

I have the king daddy and have had a few blowups but no hooked fish yet, granted I really haven't fished it a whole lot. I think the biggest advantage of larger frogs is not a bigger meal, but they provide more disturbance if you are fishing over very thick vegetation, which might make it easier for bass to key in on. 

I believe frogs are one forage where bigger does not necessarily attract bigger fish. A large bullfrog can put up a serious fight, which a big bass may not want to deal with. The large bullfrogs near me are not afraid of hopping around attracting attention to themselves, and are rather aggressive. I'm sure the occasional one gets slurped by a big 'Ol bass but I think in general they prefer the more snack size ones that they can just come up to and inhale, vs having to fight/stun a big guy.