Also, a 500 COMLEX Score (about 20-25 points below average) would probably equate to a < 210 USMLE score. From the score reporting on SDN of those who took both over the past year, I've seen a trend of:
200 usmle --> mid-high 400 COMLEX
210 usmle --> 500-510 COMLEX
220 usmle --> 580 COMLEX
230 usmle --> 640+ COMLEX
240+ usmle --> 700+ COMLEX
Of course, there is plenty of variation with what I listed above, each student is different. If one student is amazing at OMM, they might have a disproportionately high COMLEX but a lower USMLE. For the most part though, ACGME residency programs prefer USMLE since they can directly compare you against other MD applicants. A 220+ USMLE is much more assuring than the student who scores around 550 on COMLEX. For example, one residency program I saw listed their screening cutoff as either a 600+ COMLEX or a 220+ USMLE. Just to show you how one program compares one exam against the other.
COMLEX also scales crazy high when you get into the upper percentiles. The student who scores a 240 on USMLE (less than 1 s.d.) will usually score 1-2 standard deviations above the national average for COMLEX.
And tbh, if I was a US MD program director, I would be worried in using COMLEX when nearly 25% of the exam is testing on OMM, a completely unrelated subject to MD residency. It allows for great variation where someone could have a 600+ COMLEX by just being really strong in OMM and very average at everything else.