The FPS drops aren't a hardware issue. It's an issue caused by the game itself requiring more graphics/processing muscle.
Regardless, you're not seeing any lag from the FPS if you're actually getting 90 FPS. That's 30 FPS more than you'll be able to see on any standard monitor. The refresh rate of monitors are 60 Hz (aka 60 FPS). Anything over 30-40 FPS is considered playable.