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A good point. I use a Heliopan RG715 that gives a full IR effect on the MM and at a useful decrease in exposure compared to the OP's 850.The problem also is that you are using an IR filter that is unsuitable for the camera. As it passes IR in a band for which the sensor is well filtered, you will need extremely long exposures.
If you use a 092 (B&W numbering) filter your results will not only look better, you will even be able to use the camera handheld if you up the ISO a bit.