RX 580 not performing as expected. Any idea for a reason?

I just got myself a new Sapphire RX580 8GB Pulse for my older Ivy Bridge build (Z77-DS3H, 16GB, i7-3770, 650W PSU, LG 4k Screen, latest Clover)

Unfortunately it's not performing as well as expected and in Cinebench I only a get a score of 78,89fps. Most other users here on reddit had results in the 100-120fps range with that card.

Any idea what the problem might be?

submitted by /u/GoatVsOctopus
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