IMHO (maybe wrongly) I assumed there was little sound difference between the 861v4 and a G61R.
I recently sold my 861v2.81 to someone who had a 568.1 and he reported that the difference was absolutely amazing.
I can also personally report that an 861v4 is yet another significant upgrade from a 861v2.
I think the 568.1 to the 861 is the bigger sonic upgrade when compared to the 861v2 to 861v4 upgrade. Personally, I have no great desire yet to move to an 861v6 since the v4 is just superb.
So, I agree with George in that it is my opinion that your assumption quoted above is (vastly) incorrect.
Best regards
/Marcus