Animations would be the greatest draw on your system, as mentioned highly intensive target rings, but .tga's in general will not slow you down. In other words the more there are doesn't mean the slower your system will run. Server population is the biggest slow done in the game, also mentioned. Example: Sit by the MB during an a caster MGB and try to move He He..
This you have no control and even with the best system will slow you down.