6th here, I would have voted but I'm not sure I've ever heard of 6.5?
I live the sheer volume of extra stuff that came with 6th, the annuals, various campaigns that has yet to be matched in number as far as I know, loads of siege rules, a world map campaign system, boat rules, Warhammer Skirmish, online only character rules to flesh out the characters that only got a paragraph in your army books, chunky "heroic scale" models and so few models types that the conversions in the White Dwarf magazine were absolutely nuts.
It's largely nostalgia for sure, but paging through the Warhammer Skirmish scenario book really shows off the pure, unfiltered imagination that was abound at GW at the time. That book was basically a load of RPG scenarios, really turning the whole system on its head as far as your experience was concerned. The best comparison I have is the Resident Evil 2 remake 4th survivor mode. You spend all game being terrified by your opponents, barely able to match them and on the back foot at all times. Cue the 4th survivor where you switch characters and play as an absolute badass who blows the zombies away with his firepower, while his only other partner can't help but admire how cool he is. All possible because the game allows you to play like this in the main game, but never gives you enough ammo to do so. The skirmish scenario is similar for me, toning down a fantasy wargame to the individual level while keeping the rules kind of the same. If they released a book that allowed stat upgrades, linked narratives and something to aid a Dungeon Master with figuring the whole thing out, I'm sure that we could have had a really cool versions of a Warhammer Fantasy RPG that wasn't crazy emphasised on stats but easy enough to learn.
Like D&D lite