The gus offloads audio processing, whereas the sb16 requires more work from the cpu. Hence, the 3d scene at the end of Second Reality should be smoother on gus assuming a typical system of the era, e.g. 486.
This is true, but it's a small difference. It took only about 10% of a 486's CPU time to mix four to eight channels of wavetable audio. You'd never be able to notice or measure if that 3d scene was running at 11 fps instead of 10.