With a 2009 model, you're limited by the speed of the SATA connector. Yours are 3Gb/s. Newer models are 6Gb/s.
This didn't matter with hard drives, since those things are slow. But most SSDs can read data faster than your Mac's SATA connector can receive it.
What does this mean? Well, you'll notice a big speed boost, but not as big as someone with faster SATA connectors. And it's not worth paying the price premium for an SSD with faster read speeds: you won't see any benefit over "normal" SSDs.
Stick a Samsung Evo in there. That's what I did with my 2012 MacBook Pro.