About the same depending on surface.
If you look at the specs even though the cores look different they are both high RG cores with low dif. (added some similar designed balls with different looking cores)
Big Hit RG 2.63 Differential 0.020
Neptune RG 2.61 Differential 0.018
Groove RG 2.70 Differential 0.041
Columbia Wild RG 2.63 Differential 0.030
The high RG means the ball revs slower and tends to get the ball further down the lane before making the turn.
The core is like a ice skater going into a spin. A high RG is the ice skater with her arms extended, and will spin slow. As she brings her arms closer to her her speed increase same as the lower RG bowling balls. The larger and or more spread out the core(high RG) the lower the revs.
All of the above listed balls if drilled the same will roll almost identical. The main difference will be the cover stock. The neptune is a pearlreactive and the Big hit is a solid reactive. The hit should read the lanes a little sooner because of the coverstock.
You could change the surface of the hit with 1000 or 800 grit and notice an even larger difference.(earlier roll)
--------------------
" hand, don't step on the lanes without some "
