I saw them opening for Wasp in february of '87 and then headlining november of '88 with Overkill and Motorhead as openers.
Dave Lombardo back on drums
I've seen Slayer with all 4 drummers.
as far as Slayer's "vital period"? My opinion is: Hell Awaits
through Seasons in the Abyss
. and Seasons has some filler.