I do realize this is venue- and setup dependent, since the proximity effect varies with incidence angle.
Proximity effect modifies low frequency response with respect to the distance of the microphone from the source, rather than angle of incidence. Basically, it works in this way- at a specific distance, say 1 meter away as an example (realize that number will be different for other mics), the low frequency response curve will be essentially flat [edit- or rather, will match the manufacturer's published response curve]
. Closer than that and the low frequencies are boosted, further away and they are attenuated. It is true that the far off-axis response of a microphone is often different than the microphone's on-axis response, yet that difference remains more or less constant regardless of the distance of the microphone from the source. So your EQ correction will vary depending on your recording setup- you'll end up with a different correction when recording on-stage with the microphones relatively close to the sources than you would with the microphones far back in the room. And it will also vary from situation to situation and from room to room.
Play around with EQ. Try a simple low-frequency shelf filter to start, and adjust the corner frequency and boost values. Compare recordings you've made of the same jazz band in the same room with the CM3s against the OM1s. As an exercise, try to make the first sound as close to the second as possible, simply by listening and adjusting things, then once they are close, check out the values of the filter you've applied, or at least remember the shape of that curve. That shape reflects the basic response difference between the two microphone pairs in that particular situation. You can use a graphic EQ or peak filter parametric in the same way, which allows for further fine tuning of the curve, but start by approximating the shape of a shelf filter with them, and work from there. Other recording situations may call for a different curve and different boost values, but the general shape will more or less be the same. And once you've done that you have a handle a on a general baseline response difference between the two microphones.
Next is to actually dial in an appropriate EQ correction for a specific recording. The general response difference curve you figured out above may inform you somewhat as a starting point in dialing in a specific correction, but don't feel restricted by adhering strictly to it. Each situation calls for a somewhat different correction and different variables come into play. You may want more or less low-frequency information in general, or need to address a specific resonant frequency range or reduce HVAC rumble or whatever. There is no single objectively correct EQ correction for each particular recording, only a subjectively correct correction for each listener, and hopefully that corresponds closely with what you like and what you hear through your playback system.
I will say this- I rarely, if ever, find that a low-cut filter is a "musically correct" choice. Many seem to advocate chopping everything off below a certain frequency range, but I tend to hear problems with the "chop off the lowest stuff" approach even when the playback system is incapable of reproducing those lowest frequencies. Sometimes it's necessary to salvage a recording, but I always find a shelf-filter if not a more complex curve made with parametric peak filters or a graphic eq corrects low-frequency problems in far better sounding ways which don't do as much or more harm than good.
With that in mind, consider the response of your monitoring equipment when making these kinds of decisions. Since that is what you are listening through when making EQ decisions, the tendency will be to compensate for the deficiencies of the playback system as well as those of the recording. You end up adjusting things to make the recording sound great (to you) through your system. But when you listen on another system, the corrections may not sound right, and it's the part of the correction which was fixing the specifics of your playback system and not the part of it correcting the microphone and overall recording responses which doesn't "travel well". You can learn to "hear around that problem" by listening to recordings you've worked on through a number of different systems, through a few different headphones, in the car, etc. until you sort of figure out what works more or less everywhere, learn what that sounds like through the system you use to edit, and begin to use that as an internal objective reference.