Thanks for asking our advice.
The muzzle blast, flash and noise would be equal whichever gun you use, given the same barrel length. So the GP vs SP does not hinge on the gun's frame so much as the barrel length.
The 3 1/8" barrel SP would have a little more than a 4" GP, but I don't think you will notice all that much. The 2 1/4" SP a little more.
There are self-defense loads that are formulated specifically for shorter barrels.