I played around with that glyph too and some investigations showed that it is always seems to be a DPS loss as far as the math can tell.
To get a picture of how powerfull Savage Roar (SR) in itself is, picture this scenario:
You do not have glyph of Savagery, so Roar provides 40% bonus damage.
Fully Raid-buffed, flask etc all active, your DPS at a butcher fight is, say, 28k.
Thus, without Savage Roar, your DPS is 20k (since 20k * 1.4 = 28k).
For its duration of 42 seconds (at 5CP), SR increases your DPS by 8k. I.e. its total damage is 8k*42 = 336k.
If you decide to take the glyph,