So the difference would be??
BIG difference... Stuff like Atheist, Cynic, later Pestilence has technical riffs, odd time riffs, especially atheist and cynic...
North from here is STRUCTURALLY complex as opposed to being technical in terms of playing and riffs used... listen to something like Cynics "Uroboric Forms", and note how the riffs themselves are complicated, and then listen to "Fields of Blood, Harvester of Hate", and note that the riffs themselves are 80's (possibly more early 90's style though, for the heavier ones) thrash riffs, and that the way they acheive that "technical" sound is through changing the riff quite often... it's a good trick, Earlier death like Human did the same thing, not very technical in terms of the riffs or guitarplaying, but the riff and tempo etc changes heaps to give the illusion of technicality...
If you like the "Sentenced" form of technicality, in terms of structure and time changes, you might like to check out Nevermore's "The Politics of Ecstasy", songs like "The Learning" and "42147" use that same idea, cool thrashy riffs, and lots of time changes to give the "feel" of technicality, but without making it impossible to follow, like say Cynic can be at times...
hope that clears it up
-Trapped