Ref NTSB
Sitting at work with v limited access so no google etc.
Clicked my own post to check and both links are working for me.
Maybe try searching National Transportation Safety Board
Alert was issued Dec 29, 2004, Titled: Alert to Pilots: Wing Upper Surface Ice Accumulation.
Just in case you dont find it to quote two very small extracts
"According to wind tunnel data, a wing upper suface roughness caused by particles of only 1-2 mm diameter (size of a grain of table salt) at a density of one particle per square centimeter, can cause lift losses of about 22 and 33 percent in ground effect and free air respectively".
And
"The bottom line is that pilots should be aware that no amount of snow, ice or frost accumulation on the wing upper surface can be considered safe for takeoff"
i.e. you get my vote for sure.