Thank you for posting in Wired Communities. Not sure if you have check the specification of X520 and SR and LR fiber optic product brief already:
1) Intel Ethernet SFP + SR optic and LR optic product brief
2) X520 product brief , power consumption information at page 4
Please do let me know if above information meet your requirement so that I can further check for you. Thank you.
Please do let me know if the above information suffice, please clarify further in case not so that I can better check for you. Looking forward to your reply. Thank you.