Armour Question

Gear seems to come with a prefix and suffix, the suffix being dependent on the rune used.  The runes seem to have set bonuses so the more of the same rune you have equipped the different bonii you receive.

My question is, does this apply to the prefix?

Is there a reason I would want to wear 6 "Knights Armour" pieces or 6 "Berserkers Armour" pieces rather than 3 of each (assuming I wanted all relevant stats)?

Nope. The prefix just determines the stats of the piece. You can mix and match without fear of missing out on anything.

http://wiki.guildwars2.com/wiki/Prefix or in-game just type /wiki prefix