I’m not allowed to recommend a specific processor but this is the overall specs that you would want to meet to develop with UE4.
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Desktop PC with Windows 7 64-bit or a Mac with Mac OS X 10.9.2 or later
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8 GB RAM
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Quad-core Intel or AMD processor
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DX11 compatible video card
Here is a good place to go on the Forums to compare and discuss specs with other users.
Cheers,
TJ