There are over supply of GTX Cards in the market. I highly suggest to sell it the lowest price possible(Competition Wise). Because you'll never knew the next day, the price you're trying to sell it, looks over price to others. I'm one of GTX 1070 holder here that has been selling it for month. No luck at all.
I will keep my cards as there could be a sudden rise of mining profit if the market turns.
Sadly, you're wrong. There will be new cards in the market so technically there would be a huge gap between the new cards and older cards in terms of hashrate/power cost profitability. The Pascal cards will soon become not profitable for mining.