I wonder why?
Galaxy Flyer - I've seen other comments similar to yours that says "we turn of TCAS RA's when we are OEI". I wonder why?
In TA only mode, the TCAS says (and I paraphrase) "Traffic! We are going to die!" and leaves it up to you to decide what to do next. If you leave the switch in RA mode, in the exactly the same aircraft in exactly the same scenario, it will say one of a small set of messages of the form (and I paraphrase again) "Descend now or we are going to die!".
Without revisiting the caveats previously posted about what performance may be available to you, and the fact that you need to exercise judgement to not turn one emergency into another - why do you prefer the "Traffic!" message to the one with some useful additional information attached? Even OEI, you can manage most of the commands (descend, maintain VS, etc), and the only one that will make you cringe is a command to increase your rate of climb - but then you are ALWAYS going to cringe if the box just said "Traffic!".