If you look at the Marshall Street Flight Guide, a good (though not perfect) general reference to relative disc speeds and stability, you'll see that there are very few discs in their Speed 8 category. Some of this is their ratings: most have the MVP Amp as Speed 8, but Marshall Street put it in Speed 9... but I digress.
What many people do in putting together their bags is skip a speed number. The (Speed 7) Teebird and Eagle are huge sellers (as are those of other brands, but I'm using Innova as a reference). The Speed 9 Valkyrie was once the world record holder and is one of the most popular and best selling discs in the world. The (9) Firebird is very popular as well, as are the Roadrunner and Sidewinder.
...