NEVER take more of a medication than is prescribed! Doing so put you at risk of respiratory suppression , overdose, and death. It is also abuse of a prescribed medication and will result in an abrupt dismissal by your doctor and likely being refused treatment by another doctor for pain.
Overdose can and does occur with subutex just like any other opiate.
If you require something more for extreme pain you need to discuss that with your physician and let him determine what you should do.