Tricky. There isn’t really a way to not use the RTX hardware with OptiX 7.
At least BVH traversal will always be part of that, and triangle intersection in addition when using built-in triangle primitives.
When benchmarking an application, the resulting number of rays per second would be one of the indicators, but these numbers greatly depend on the ray divergence and amount of time spent in your own functions, means everything outside the BVH traversal and triangle intersection.
You could implement a custom triangle intersection routine and compare benchmarks using that and the built-in triangles and see how the per-function Nsight profiles change in relation.