This thread is showing fitment for a NBS model. Mine is a NNBS (09 Sierra).

 

I've read that 1 3/4" vs. 1 7/8" article on LS1tech, it does show on the graph that at lower RPM the 1 3/4" are better for torque roughly the same for HP. It evens out around 2500-3000 RPM and then 1 7/8" take over with larger in both HP & torque I believe. I thought the article was in relation to a magazine, but im having trouble remembering. Obviously dependent on motor/heads and work done.