Upgrading from OptiX 6.0.0 to 6.5.0 is definitely recommended.
Note that since OptiX 6.5.0 the OptiX core implementation and the denoiser ship with the display drivers and that means you get bugfixes and improvements with each driver release and there have been plenty in the seven months since OptiX 6.5.0 was released.
The PTX parser in OptiX 6.0.0 might not have been updated to the newest available SM version. This happened before, see: https://forums.developer.nvidia.com/t/rt-error-invalid-source-when-using-sm-61/53948
You should be fine when limiting your SM target to the minimum supported Maxwell GPUs which is SM 5.0. Even Kepler’s SM 3.0 will do as long as the CUDA toolkit supports it. OptiX rewrites the code internally to the underlying SM version and the final PTX assembler will optimize it again.