The 265 only requires 1 PCI-e power connector, the 270X requires 2, so if you have a weaker power supply or are planning on putting it in an HTPC the 265 may be the better choice.
Sorry, I linked the wrong model initially. I suspect the R7 265 is still reporting to Passmark as the HD 7850. Which would account for there not being a specific benchmark for that device.
The 265 only requires 1 PCI-e power connector, the 270X requires 2, so if you have a weaker power supply or are planning on putting it in an HTPC the 265 may be the better choice.