hehe... this is exactly the reason we are upgrading the renderer. The new version can handle many more lights and shadows with a lot less drop in performance. It is taking time to get this new version ready, but we should have an alpha for you all the play with in the next couple of weeks.
For now, on extra lights, disable shadows to increase performance.
GeForce 9600GT
We used to run this card before we moved to the GTX460 and GTX560ti and i would consider that card a bottom end card for a modern game/game engine.
20 fps was a common occurrence on that card but we still managed to make some cool looking scenes and levels. I look forward to seeing your frame rate on the new version using DX11 & OpenGL3+ as long as you can run DX11 or OpenGL3 as the new renderer is dropping support of DX9.