It depends on which burn rate chart you look at. Western shows #9 as faster than 2400.
Charts do change and vary.
What do you mean they ONLY have data for 38 Super +P?
In the western manual I linked page number 9, it goes from 9mm +P, to 38super +P, to 357 sig. no standard 38super loads.
Please define what you mean by 'perform well'.
By perform well, I mean it may not fully burn, or burn cleanly. And that it will provide velocities lower than listed and or expected. It should work and be safe but will most likely perform poorly.
Speer seems to think #9 is fine in the 38 Super. They have load data with it for 115, 124 and 147 grain bullets. Their data shows #9 producing the highest speed with 147 grain bullets.
Lyman also has #9 data for the 38 Super.
And Hornady shows #9, like Speer, producing the top speed with 147 grain bullets.
I added some info to my above post with all the data I have from my sources.
As you noted #9 seem to perform well with heavier projectiles, as was my experience with #7 in 9mm....