b16 pistons have more dome than gsr pistons - quite a bit more in fact.
If the dollars are going to work out the same, it's a no-brainer. The gsr bottom is the way to go for the extra stroke, bore over the b16.
Lots of variables, but figure about 6 to 8 lbs of extra torque and 10-12 more hp depending on which pistons you end up going with.