That is the stock RAM for the G55/G75. Two weeks after I purchased my laptop, I did the same thing you are referring to. I wanted to max out the RAM, yet I wanted it all to match. So I hopped on ebay and found the IDENTICAL stock RAM. I got 2x 4 gb of the stock RAM for 35.00 with free shipping. If I were you though, I would go for 2x 4gb of it as I did. If you are going to order it, you may as well max it out. The link you have shown is for a 2gb and a 4 gb stick.
Here is an auction with what you are looking for. Only an hour left though...