I would suggest taking some practice and work on the timing for your game.  Timing is everything if you ask me.  

To moderate my speed, I tend to hold balls higher or lower, and move myself closer or further from the foul line.  For more speed, I'll take a few inches back and hold the ball a pinch higher, and it will speed up my delivery and usually give me about 1 MPH more.  For reference, I average between 16 and 16.5 at the pindeck.  

If you still have speed issue that are messing things up, I would practice with a friend's 16lb ball and see how it works out for ya.
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Proud Supporter of Rob Stone
Obviously, you aren't a golfer.
Some stayed in the foothills, some washed logs like teeth.

who knows, you throw 18 mph but do your rev match up or do you have more revs than speed?going up a pound will not make a difference.

One pound makes a huge difference in deflection IMO.  Does your ball look like it takes out the ten after hitting the pocket?  I moved back up to 16 mostly due to the center having first generation synthetic lanes and Twister pins.

The other thing to consider is consistency.  While slowing your speed down due to the extra weight might increase you accuracy the first game, you may tire easier and throw much slower the third game.
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Where is the bait?  I'm goin' to jail!!! - Chocolate GAYzer