You don't say what size hex and how much has to be turned off. If it is possible based on the size and rigidity of the material to machine off the entire hex in the first cut this can help with tool life. The only other thing is moderate speeds, DOC enough to get under the work hardened surface and feed the same. Rough figures could be 250 SFM, DOC not less than 0.04" and feed not less than 0.005".
Given the option I wuld pass but then I am a chicken heart when it comes to stainless.