Ilford shows this to be an ISO 1000 speed film.

Whether to expose at 1000, 1600, 2400, 3200, or any other speed depends on what you want for shadow detail, and how flat the lighting is or is not.

Generally, indoor scenes are flat and can tolerate some expansion during development, resulting in slightly increased speed. Also, your choice of developer can influence the speed.

Realize that exposing at 2500 is just one-third stop under 3200, not a significant change.