More RAM will not boost your computer's speed, per se.
Your computer's speed will remain the same as it is now.
You will only notice a difference if you are using RAM intensive apps. Games are RAM intensive, and may run smoother with more RAM. Not because it makes the system faster, but because it won't have to swap to the RAM and HD so much.
So, if you are using RAM intensive apps, then you may notice a bit of a boost in that app's performance.