The main difference:
Bitcoin Gold is better to compare with a Litecoin fork in 2011. We can say that it is abosolutely new altcoin, with a different from bitcoin cryptographic algorithm, and they use main blockchain just in porpose to issue initial coins. You can easily get your BTG, if you keep your Bitcoins on one of the exchanges that supports BTG or on wallet where you control your private keys (Bitcoin Core, etc.)
And the main idea of SegWit 2X is to improve the Bitcoin Blockchain and solve the problem of scaling bitcoin network. I believe that we wont see a split up in the middle of November, but if it happens, we will see two separate coins B2X and BTC (B1X).