Both balls would be stronger than the Virtual Gravity. The Grudge would be stronger overall compared to the Ultimate Nirvana. The Grudge comes at 1500 grit from the factory, and the Ultimate Nirvana comes at 4000. If they were drilled the same, the Ultimate Nirvana would go about 3 - 4 feet longer than the Grudge and have a sharper motion on the backend. Both take well to surface changes and can be adjusted to fit your game. Either would be a good choice.

Brunswick uses a generic core shape in their 12 & 13lb balls, however the RG and Diff are similar enough to the heavier weight balls that they can be drilled using the same layouts you would normally use.  It is important to keep in mind, however, that the ball motion will be slightly different than the heavier weights.  You may see something that goes slightly longer on the lane due to the slightly higher RG of the lighter weights.

Due to physical issues I throw 12lb stuff.  I have a DV8 Endless Nightmare that has a horrible reaction despite a very aggressive drilling [it is going out in the trash soon.]  Virtually no movement on the lane regardless of cover preparation (dull, matte, polished, etc.)  However, I have a 12lb pin-up Radical Primo that totally out performs the Endless Nightmare despite being a much less aggressive piece of equipment.  My 12lb Storm Virtual Gravity Nano from a few years ago (drilled 4x4x2) was an absolute beast.

I have been reluctant to try the newer Storm Premiere line offerings in 12lb due to the lower diff numbers.  I have some concerns about getting them to turn over in the backend to generate a consistent strike angle (which is crucial with lighter weight stuff.)

Another option is that you can always check out Motiv.  A big difference in their product line is that they don't use generic cores in their lighter weight bowling balls.  They use the true core as the heavier weight balls have.

2 options you would have in their lineup would be the Revolt Havoc or the Primal Rage Remix.  The Remix will definitely be stronger than the VG while the Havoc would probably be a bit closer overall in shape and strength.

The primary reason for the higher RG numbers in the lighter balls is that with a lighter ball, the hand will tend to accelerate through the ball with more torque than it will with a heavier ball. In order to try and replicate the ball motion of the heavier ball, the RG must be raised.

thanks to everyone for your help....I will be getting the Revolt Vengeance after much considerations......hope this will be the right choice.....I think it will fit nice with my current motiv line of venom toxin and forza redline

The Vengeance is a great ball. Enjoy!

...Due to physical issues I throw 12lb stuff.  I have a DV8 Endless Nightmare that has a horrible reaction despite a very aggressive drilling [it is going out in the trash soon.]  Virtually no movement on the lane regardless of cover preparation (dull, matte, polished, etc.)  ...

Just as an update, I took my Endless Nightmare back to OOB finish (500/1500 siaair) and am now having success with it.  Some balls take great to surface changes, others don't I guess.  Ball definitely NOT going in the trash

I have found that in terms of lightweight equipment, Brunswick brands (DV8, Radical, Brunswick) work the best for me in terms of lane reaction and carry.  Don't be scared off by their generic core shape.  In fact, other than my spare ball my whole bag is Radical and DV8 right now, while everything else (Ebonite/Track/Columbia, Motiv, Storm, Elite) is sitting on a ball rack in the basement.