3x18650 IMR cells are going to be likely to flash the 1185, unless you terminate the charge prematurely. We've had a number of reports of flashes even on 3x protected 17670s in M6 setups...
I would personally suggest 3x protected 18650s for the 1185 as this will reduce the chances of insta-flash compared with the IMR cells, and since the load is ~1.5C for for this size cell, there isn't really a lot to gain by going with IMR cells. IMR cells should be considered for options where either the maximum safe current of a LiCo cell is being approached or exceeded, or you're going to be bumping up against the protection circuit with the load.
I have personally never been a huge fan of the 3x17670 protected cell configuration driving an 1185 as this is technically over 2C for most 17670s out there. But.. it's not over by much, and if the cells are used in shorter bursts most often (which is usually the case with this type of heavy hitting flashlight) then it's not that big of a deal... With that said, a pair of 1 cell extenders on an M4 with the 3x17670s is an option. The 3x1860 leefbody would reduce stress on the cells substantially, while increasing runtime by quite a bit. (~40 minutes compared to ~25 minutes).