SSD drive--isn't the recommended 6gb replacement too fast for my mac?

I have a MacBook Pro 15" Core 2 Duo Models A1226 Santa Rosa 2007.

I do not understand something about data transfer rate in regards to me buying a new ssd hard drive from IFIXIT, which I want to do to speed up my old Macbook pro. From what I do know, the Data Transfer Rate is the rate at which data can be sent or received. This is determined by your motherboard. A drive with a higher transfer rate will only run at the rate of the motherboard's transfer rate.

If this is true, how come the ssd ifixit recommends for my Macbook Pro is a 6 gb one? Isn't this to fast for my old computer? Would it even work? Wouldn't a 3 gb ssd be better? Or perhaps even that would be too fast? I think my data transfer rate on my Santa Rosa could be even as slow as 1.5 gb. So I am very confused. Could somebody let me know if I would even benefit from upgrading to a ssd, and if so, what would be the best one for me to get?

I've read on other site and others when people put these "recommended" 6gb ssd drives in 2007 Santa Rosa machines like mine, they do not work. If this is so, why would IFIXIT recommend these drives for my machine. COLOR ME CONFUSED!! Please help.