If the psu has the capacity for 2x EPS, I'd use both. Those connectors supply the cpu with supplementary power, having both will not hurt, having just 1 might under full load, full turbo power draws.
A single 8pin EPS is rated for 288w, so physically capable, but that's putting entire reliance under heavy usage on all 4 pins for power/ground use. Better to be safe and spread the load out.