I could tell you right now that only 30% of the bitcoin community (If not less) are aware of this hard fork, It has no mention in Reddit, and most news sites (unlike SegWit2X) so I doubt we will see any significant price decrease. In fact, If there will be a chain split, there will be a price increase because everyone would like to get the equivalent in BTG too (free money). The same thing could be said regarding 2X, people have seen how BitcoinCash affected the price so they won't fall for this twice.