I have an old Dell T5500 that I use as my main PC...mainly for gaming. It has the following specs:

CPU: Xeon X5550 (4 core/8 thread @ 2.66 GHz, boost to 3.06 GHz)
GPU: RX 480 (8gb)
RAM: 24gb
SSD: 500gb Samsung Evo 690

I'm thinking about upgrading my CPU. I'm trying to decide between these two:

X5675: 6 core/12 thread @ 3.06 GHz, boost to 3.46 GHz. (about $30)
X5687: 4 core/8 thread @ 3.60 GHz, boost to 3.86 GHz. (about $30)

There's also a X5680 that I might consider that's around $45.

Comparison: https://ark.intel.com/compare/37106,52578,52577,47916

I'm leaning towards the X5675 for the additional cores/threads but the X5687 has the higher clock speeds. Note that the Dell T5500 can't overclock so I'll be stuck at stock speeds. What do you think would be the better CPU? Or should I just stick with the X5550? Thanks for your advice.