Jeff, just adding a bit to what Tak has written.....
The two rods you are looking at essentially cover PE4-6 but I would suggest you're looking on the lighter end of that scale, particularly with the 84/18. If you're thinking of loading up with PE6 and you want to go hard against a fish, I personally think you better bring the 80/35 into the equation. Carpenter have the 80/35 marked as PE5-8. I suggest that it is an ideal PE6 kind of rod.
I note you mentioned fish up to 25kgs. A 25kg YTK is an awesome beast already. Even on a 83/40 on PE8, a fish of that size is going to be a challenge, particularly in the environment these things live. In terms of the rod's ability to handle GTs of the size you mention, I will emphasise that they were not made for GTs. It's a little scary for Tak to contemplate people going out there, loading up a 84/25 with PE6 and going hard on GTs