Dave, dude, don't be one of those guys. Last thrash gig I went to there was a guy in the queue ripping the piss out of some young dude who hadn't heard of Heathen, and I just thought "what a fucking twat". It's not like Heathen or Mutant or Artillery ever get any mainstream exposure in the media or anything, so generally people hear about them by speaking to people on the internet. Stupid cliquey know-it-alls who take the piss like that will just put people off good music in the long run... We all found these bands ourselves, now it's MSD's turn. Don't get l33t on his ass!
As it happens MSD, Dave is right. Try both those releases, lashings of goodness in each!