This CPU isn't suitable for modern games, and it will really bottleneck above graphic cards, there is no sense of buying them for that cpu. You should firstly upgrade your processor - depends how $$ you have to spend, but the best would be some balanced set. Even modern Intel 2-cores Pentiums and slower AMD block the full potential of such gpu in most games.
Of course if you gpu is really old then you will see difference, but still most games will be unplayable cause the heavily depend on cpu. if you will ready any benchmark comparison note what CPU they are using in it.