Each is overclockable, as well, but, I did not head down that debate path...
The 2600K is not going to last forever, to be sure...; but, this is not an upgrade from an 8350, either...
But, imagine slapping in a $600 upgrade, firing up your favorite game, and getting what could be a 1-2 fps gain...; the gain over hypothetical 2500K would be more noteworthy because of the jump up from 4c/4t.
Now throw streaming while gaming into the mix, and the 1700 as an 'upgrade now' makes much more sense...
But, were it my money, and pondering an upgrade from a 2600K? I might be tempted to stand pat and evaluate 8600k/8700K performance in Sept/Oct....
(The R5-1600 games about as well as the 1700/1700x/1800 when all are run at the same clockspeed...