This may seem like an odd question to ask, but reels like the Scierra XDP+ or Snowbee geo 7-9 reels are marked as able to load 7-9wt lines correct? Well i used an xsd reel a couple of years ago and loaded a 10wt spey line on a 7-9 reel with gel spun backing fitted.
I know a lot of people were put of saltwater fly fishing due to expense of reels and spools ect. I have just loaded a new geo 7-99 with my 7wt trout lines and no issues as expected using standard backing and loads of it at that lol...
I have loaded a Hardy Swift 1000 with a 7-8 switch line that has a long belly section almost like a shooting head or spey line again. Measuring the spool depths and angles ect on both reels there isnt a lot of difference in them at all.
Thus enabling me to carry a full set of 8 and 10wt lines for uk use for pike and saltwater for £10 a spool little extra expense but a whole world of new fishing to explore for people.

Tropics fishing however is different much bigger species and a dam site more backing may well be required but less lines usualy floating and intermediate in my experiences.
Just though i would ask if anyone else lines up above reel ratings with gel spun or is it just me?

Tight lines all