if u sell that card and you will buy an hd 7870 so that will not be an upgrade because there is not a big difference between hd 7850 and hd 7870.
if u get second hd 7850 it will be an good move you will get a very good performance.:)http://www.youtube.com/watch?v=7BeKb9M5zV0
if u think of selling that card then get a gtx 670 which will said to be an upgrade and there will be no issues with drivers if u will use older driver which is working with your card perfectly then u will have no problems.:)goodluck.:)