Published Data on Critical Temperatures for Grapes

This is all I've found published with empirical frosty-grape data. 

From Frost protection: fundamentals, practice and economics
TABLE 4.8
Critical temperature (T_c) values (°C) for grapevines

Grape Winkler, 1974	New growth:			-1.1
	Woody vine:		-20.6	-
		French hybrids	-22.2	-23.3
		American		-27.8
			10% kill	90% kill
Grapes (cv. Concord) Proebsting, 1988	First swell		-10.6	-19.4
	Late swell		-6.1	-12.2
	Bud burst		-3.9	-8.9
	First leaf		-2.8	-6.1
	Second leaf		-2.2	-5.6
	Third leaf		-2.2	-3.3
	Fourth leaf		-2.2	-2.8

The upper data set is from Winkler's General viticulture, 1974. 
"Temperatures (o F) Effects Down to 30o F If preceded by warm weather and rapid growth, some killing of the most rapid-growing shoots observed.  Damage usually slight if of short duration and if occurring during period of cool weather. 26o - 30o F Extent of damage related to duration of cold, daytime temperature preceding frost, growth rate, variety, and minimum temperature reached. Below 26o F Will kill all shoots, flower clusters and even partially-opened buds if duration is a few hours or more."

The second set of data is from 'Critical Temperatures for Concord Grapes" by E.L. Proebsting, former Washington State University horticulturist, Brummund and Clore (1988).  The data was probably collected in 1977, using in laboratory equipment.  Samples (cuttings or live plants) were placed in refrigerators and exposed for several hours to a test temperature, then removed.  After 4 or so weeks, the 10% and 90% kill assessment is made for the given stage of growth and temperature.