I would strongly recomment the 4670 Sapphire with DDR4 Memory. I did a lot of research, and found the faster memory helps over the overclock of the HIS Iceq GPU. Also, if you have a well ventelated case, you should not have any problem overclocking the Sapphire DDR4's GPU 30mhz where the HIS is clocked at. There are some pretty good reviews, I will find and post here showing the above. Also what brand is your PSU with only 300 Watt I would suggest strongly the 4670. the 4770 will probably be a bit to much for it.