http://www.ec.kingston.com/ecom/conf...R400X64C25/512 http://www.ec.kingston.com/ecom/conf...VR400X64C3/512
There isn't a significant difference between the two, would you be able to return that stick and buy exact same one?
The first stick you bought looks to be better and have a faster set of timings on it, you should be ok. However if you have the option, it would be best to use tthe same sticks.
I would suggest going ahead with the extra $15 dollars for the better stick.
Kingston value ram is good stuff and both should run ok together, however they still sell both sticks so it would be easy enough to get the other stick instead if you can still return it.