Firstly, all you need to do is find the lowest flash point of any of the fatty acids and you're set. Because saturated fat enters a denser conformation than unsaturateds or poly (because the atoms of saturated fat follow a specific pattern as opposed to others), you're likely looking at the poly's for the lowest FP because they will be the least structurally 'comfortable' in the whole molecule and well, as soon as one of those ignites the whole temperature of the fat will rise to the point of ignition of everything else.
Ah! And here we go. http://en.wikipedia.org/wiki/Flash_point
- look at canola oil. 620F. Since canola oil contains a very high % of monounstaurates, you know that at 620F this part of beef fat will ignite. Now because of the %s and the fact that the freezing point of canola oil is 0F whereas that of beef fat is somewhere in the 100-120F range (just from practical observation - I've never seen beef spontaneously melt on a hot day), I'd say yes, you were rather close. There is an equation for determining a given ignition or boiling point from physical chemistry which states that in a mixture you take the partial fractions of everything and -then- multiply by that a factor of less than 1 (because of the molecular chaos), my guess is something like:
620F + ~150-200F * .95 or something (to account not only for the mixture we know of but also for cholesterol, which is another molecule that destabilizes the overall stability of the mixture) = ~760-780F.
Of course, the other thing you can do is go to a chem lab, use a fumehood and go nuts with a heating coil, a metal pan and beef fat if you need perfect numbers.