You honestly believe that a card which is currently going for £500 new will be able to be bought at more than 60% mark down second hand just months later? Even putting aside the performance difference between the 980ti and 1070/1080 for one second (which you can't ignore anyway), when has this ever happened ever in the history of GPU's?? Prices WILL drop, no question, but some people need a reality check.
Yes, and it is the people who think the 980Tis wont drop ( £200 is maybe a bit extreme but probably £250 second hand.
The 780Ti was still selling for £500 right before the 900 series came out. Then weeks after it was being sold BRAND NEW for £300 to get rid of stock. the 970 was snapping at the heels of it and only cost £270 brand new so 780Ti second hand prices obviously plummeted.
The same will happen his time around (ie the same thing that happens every generation)