Yep what one calls medium another might call light medium and so on. It's all so subjective.
Take the Visionary ball comparison page.
http://visionarybowling.com/?page_id=270Visionary puts the NBPP weaker than both the Ogre Pearl and Gladiator Solid. While BTM rates them OOB as.....
NBPP torque 6.5, length 12.5, backend 15.0 and total hook 49
Gladiator Solid torque 6.0, length 12, backend 14.5 and total hook 48
Ogre Pearl torque 6.0, length 14, backend 15.0 and total hook 47
I would agree more with BTM's opinion in OOB surface same layout. So for me NBPP for medium-heavy, Gladiator Solid same, Ogre Pearl medium, SS Ogre and G/B Centaur light-medium.
Here's the kicker if one grabs at the bottom all these balls can be something different for many folks add ball speed yadda yadda and we all may get different ball reactions. The grabbing at the bottom and coming around the side of the ball can vary ball reactions widely. I get to bowl with this equipment on various patterns in tourney's so my opinions are based on more than one house on one THS lane condition.
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Scott