there hasn't been any major differences since r 4.5 imo
R4.5 is exactly the same as R4. I don't think there have been any other changes since then, either. Maybe some tweaks to the stem colors? I can't remember exactly when that happened.
As for the older versions, honestly they were still great. R4 the stems changed to reduce wobble but, IMO, the wobble in previous rounds wasn't more noticeable in actual usage than any other switch.