You might have the wrong version numbers.
v4 corrected the "pop" and audio amp issues, there were no changes to the RF sections to address the later found spurs and harmonics issues.
The v3, v4, and v5 boards, the v5 are the ones that are best for spectrum purity. ARRL Labs reviewed and found them to be in compliance, though some on this forum did state that their measurements did not agree.
v6 is the current version. This one has pretty much the same components as the v5, the difference is the change in the stock display, Raduino and main board layout. There are also changes in the board layout that do away with any soldering, at least as far as a stock radio getting on the air.
I have not purchased the v6, as I already have a v5 with a 3.5" Nextion display, so not much reason to go to the v6 with the touch screen. I also have 2 v4 boards with Nextion displays (bought the second to act as a backup and base for comparison of mods board). Not much difference in performance between them, and each seems to operate about the same. I would recommend the v5 board if available, as that version would not need the mods to correct signal purity issues.
FWIW and YMMV