Did almost the same upgrade 2700k at 4.8 to 6700k currently at 4.6Ghz. FPS improved aound 40%. Maybe partly due to moving from 780ti to 980ti overclocked. Taxiing around UK2000 EGKK, Orbx England, UT2, ASN, same settings as before.
FSMark11 suggests 6700k at 4.5Ghz has same performance as 2600k at 5.2 Ghz.