I've tried to speak to everyone that has shown interest in tactical games/sims.

The playlist so far:
Swat 3,
Swat4,
Rainbow Six 3:Ravenshield
Ghost Recon

Splinter Cell series TBD.

Other than the newer Splinter Cell titles, everything on this list came out between 1999-2008. You should be able to run all titles on high unless you are using a calculator. Swat 3 is 1 GB, ravenshield is maybe 6-7. Not a lot of space overall, pending your hardware.