It all depends on how you read it. Even in Efle's model 507 and 508 are clearly ABOVE the 29 marker. I can't think of any chart ever where you are supposed to interpret scores that land ABOVE a marker as equal to that marker. In other words, there are no differences in the charts other than how one designates scores that fall above the old hard numbers and below the next hard number.
Now, psychologically speaking, if I had a "hard" 29 on the old test I would want what counts as 20 on the new test to go as high as possible, and I would be invested in adcoms viewing my old 29 as a 508. If I have a 508, I am of course invested in that 508 not being reduced to a 29.