Take a few rides to get used to stem length changes before you make a final judgment. Even a small change requires you to reposition your body over the bike, which usually feels "wrong" at first.
Can't feel a difference? Instead of making a small, 10-millimeter change, go 15 or 20 so that you'll experience a dynamic difference in handling. You'll probably find that scaling back to a stem length half-way between the new extreme and your old standby will be perfect.
Choose a stem made for your riding style. A super-lightweight stem may work well for a lightweight rider who has proven not to break anything on his bike. That same part, however, would probably be a ticket to the hospital's emergency ward for a FR/DH specialist. Always match the part with your bike and your riding style.
Be sure that your new stem installation will not cause the brake hoses or shift cable housings to bind when the handlebar is turned full left and full right - or when the fork is fully extended, in the case of adjustable-travel forks.