I remember when IMC came out that Aliied company got with Greenlee and went to demonstrate the difference on bending and I believe IMC had more deflection than RMC. They then tolds use to back out the dies when threading the conduit to reduce over cutting. Also explained how it was tested to match the charitistics of RMC and if I remember correctly they matched identically even the explosion test. My only advice is use what you are comfortable with and easily to obtain. As the Electrical Contractor on the job you and your crew will be the only one who knows.