I agree in the flaps extended case but I'm sure I've seen lower Cl on flap 0 + slat vs no slat.
Remember we are talking about off design geometry following a flap failure.
Here is an old but interesting report.
http://naca.central.cranfield.ac.uk/...ca-tn-3129.pdf
Last edited by FE Hoppy; 20th Feb 2017 at 22:01.
Reason: added link