Interestingly, EASA stay with the old equation, but there are many other considerations involved in landing.
Operation on Contaminated Runways.
The Canadians have done a lot of work in this area –
Overview of the Joint Winter Runway Friction Measurement Program, November 2004 (TP 13361) Most of the references are available via Transport Canada web site.
And one more equation
Vacq(kt) = SQR(tire press / sg of contaminant)
Ref
Getting to Grips with Performance see page 82; an Airbus document (8mb)