Don't fall prey to the pseudo-hardcore poser roadie BS. If you can ride comfortably with the stem slammed and it doesn't take away from your power or breathing, then do it.

Hurt your back one good time, and you'll ride it jacked up again. Hell, I ride 25mm of spacers with a 100 degree rise Thomson X4 stem. No change in position, other than higher hands and the back doesn't hurt a bit.