Andrewkovala,
The long-belly AFFTA spey line standard has 800 gr @ 80' for 9wt long-belly lines. The 8/9 true long-belly lines (i.e. lines with bellies of 80' or longer) made in North America and Japan are now and have been based on this standard for about 8 years or so now. Such lines are really 9wt long-belly lines and weigh in somewhere between 770 grs. and 840 grs. (perhaps a little more if the belly is 90' or longer). This is why a rod such as the G.Loomis Grease Line series rods that were desgned to cast long-belly lines and are rated for the AFFTA long-belly line standard as to line wt designation work well with mid-belly and long-belly lines within about 40 grs. up or down from the AFFTA long-belly spey line standard.
The 8/9 long-belly lines weigh in around 800 grs (in other words they are 9 wt long-belly lines). However, the mid-belly 8/9 lines are too light to load a rod that works well with an 8/9 long-belly; therefore, you need to go up on line size to the 9/10 to get the line weight grainage up far enough to properly load the rod but not overload it. And the various 9/10 mid-belly lines made or sold by North Amercian line makers or distributors are really 10 wt mid-belly lines.
I know this can get confusing; but if folks take a little time, look up the AFFTA spey line standards, print them out for future reference, and then look at them when looking for a line that would work on their specific spey rod, the confusion would pretty much vanish. I've got to let you know that I much prefer having the grain window the rod was designed to cast well marked on the rod instead of the AFFTA spey line wt designation because it make it much easier to match a line (provided the manufacturer puts the line's belly grainage on the box).