If you wait for sales and use coupon codes, you can get plated for $36/500. Even ordering in bulk (4000) from Everglades, I'm not seeing jacketed for under $44/500.
To the OP: Couple things.
The OAL listed in the book is just the OAL the guys making the book used--
using the bullet that they used. Their 115-gr roundnose is probably not the same length as your 115-gr roundnose. And they frequently will select an OAL shorter than anyone would reasonably use, to provide a "minimum" OAL in their data.
In other words, if they tested my 9mm, loaded out to 1.160", well...that wouldn't provide useful data for anyone that had to load shorter.
Second thing--.5 grains from "start" to max is really not that small. Some powders are more sensitive to low charges than others, so the starting load must necessarily be closer. That said, you'll note that most of the powders used in 9mm--many of which are quite suitable--have very low spreads, mostly in the .5-grain range. 9mm is a high-pressure cartridge with a very low useful case capacity. If you look at, say, .38 Spl or .44 Magnum data, you'll notice a much wider spread.
Ordinarily, if I see that most powders in a given cartridge have starting/max spreads of, say, 1.5 grains, and Powder X has a spread of only .5 grains, I consider it to be a sign that Powder X might not be particularly suitable.
For quality plated bullets--basically, anything that's not minimally-plated for anti-lead regulations at ranges--I usually use jacketed data. That said, I also look at lead data, and if I'm unsure of how to proceed, use the area that overlaps if possible. In this case, we can check out Hodgdon's excellent online data.
Set your sights on pistol reloading data | Hodgdon Reloading
A 115-grain lead bullet is listed for 6.4-6.9gr of HS-6.
A 115-gr jacketed bullet goes for 6.7-7.0, and tops out at 1234 fps, which means it's still slow enough for plated.
Hence, I would probably roll with 6.6-6.7 gr.