[Spey Salar]

I don't know your rods, but I have used these lines on others. I think on the 12'6" 7/8 either the 525 or the 550 would work depending on the load you prefer, I'd try the 550 first. For instance, on my Burkheimer 7134 the maker recommended a 525 Zone, but several users have reported they prefer the 550. A matter of personal choice. Nextcast lines can generally be a bit heavier than others and still cast well.

Nextcast's website has recommendations which usually are close to what is needed.

I think the 40.8gr Salarfinder head you mention is the SalarFinder Single fully integrated head which INCLUDES the tip. On that one you would not add an extra tip to it. The 9/10 Salar Finder regular line is 35.6grams to which you would add a tip like you indicated. The 10/11 regular line, not the integrated, is 38.9 grams. The Salar Finders are not designed for heavy tips like the Coastal or Zones. Tips should be between 8-11 grains/foot. So the Guideline tips at 9grams/138grains should work ok.

You could use the Zone on the 14.6, either the 625 or 650 would probably be good.

Note that Nextcast gives ratings on it's website, but the recommendations on the Zone are for American rated rods, the Salar Finders are rated for Euro rods. A bit confusing, but generally American ratings are heavier than the Euro equivilent, i.e. a 7/8 Euro rod is sort of like an American 7, while a 9/10 Euro rod is sort of like an American 8/9. This can vary of course depending on the individual rods, but it gives some guidance.

Nextcast lines are great, but they have always been a bit confusing in their ratings charts. The good thing is that if you make a wrong choice, the lines are popular and you can usually sell them without losing very much.