In preparation for 6th ed, I've been boning up on 5th ed, having not played 40k seriously (or at all) since 2nd. And, I have to say, without having actually played it, I think that 5th as a ruleset lends itself to a far greater level of tactical maneouvre than does WFB 8th. Like I say, though, I haven't actually played, so I have no idea about metagame and whatnot.
(additional caveat: I find 8th... not so tactical. It feels like they're attempting to add complexity through increased randomness, which I find problematic at a level of game design. I find the decreased emphasis on movement necessitated by the massive units we're fielding slightly boring, and the body count as a result of the step up rule effectively negates intelligent use of static CR. I still like it, of course, or else I wouldn't be playing it. But it's less like chess (or even Catan), and more like Uno).