8GB 1333mhz SODIMM in Macbook Pro 13" 2010 (7,1) alongside original 2GB stick
It should work, but it's not recommended.

You should always use the same module, also I believe that way you got some performance benefit. MacRumors has a post about this.

Also, I believe your MacBook Pro won't support more than 8 GB of RAM according to the post, but that I'm not sure. Check out Apple's guide or technical documents for these information.

Another thing to be aware of is if your machine supports 8 GB on a single stick.

This is what I suggests. Buy two matching 4 GB 1066 MHz DDR3 RAM for your MacBook Pro. That way, you won't get into any trouble. It might cost a little more, but it's much more reliable.