UPDATE
YES!, I finally did it!, and found what I think is the key to getting the heavy hitter achievement/trophy with a 2H warrior, cause I'm doing over 250 alot now. Level 17 in the Brecillian Forest after doing all other main quests. Werewolf was my first target, I did 256. Right after I did 289 on the great bear, 278 on Ogre, 272 on Sylvan tree, 290 on another great bear, and believe it or not 331 on the grand oak boss!
The most important things in common for all these was having Assassin talent engaged on my enemy from Rogue companion, as well as, Vulnerability Hex from Mage. I was only getting 208-240 without these on target.
The essential talents I had engaged for my 2 handed sword warrior were Beserker and Blood Thirst(warden's keep). Perfect striking doesn't seem to help, so I learned I really don't need to invest in it. Just as important is having Warden Commander armour(warden's keep dlc) with Executioner Helm(you can get from Cesar's special stock in Denerim, after you do all the Crows quests but don't kill Master Ignacio after, or Cesar dissappears from the market). This is the best Stamina gear in the game. My belt was Andruil's Blessing(from Mage quartermaster) with Harvest Festival Ring(stone prisoner/honnleath) and Key to the City(Orzammar) ring. I was using Starfang 2 hander.
Had spend all but like 3 points in strength, had bought both talent books, and got all fade stat increases from mage tower quest. My stats were STR 83, DEX 24, WIL 25, MAG 16, CUN 21, CON 23, was Beserker and Champion.
So, stack Beserker, Blood Thirst, then have Rogue engage Assasin Mark, then Mage engage Vulnerability Hex, then immediately engage Final Blow on target. It worked all but 3 times I've tries it so far. The last key to getting it, I think, is the fact that I was facing enemies with less defense/armour. As I stated, I was using almost the same set up at the end of my last playthrough and only did 246 once, but it was in the Alienage and Final Battle against more heavly armour/defense foes and I didn't have both Assassin and Hex on target, often.
Feel alot better now and hopefully this will help someone who's having alot of trouble getting it, like I did,- with 2 handed warrior. I have put over 200 hours into the game and this was my 3rd full two handed warrior playthrough.
Thanks so much to Bioware for giving us another- TOP RPG EVER quality of game, that we'll be playing right up until the sequel. This game is even better than when Jade Empire came out and has rivaled the experience and awe I had with playing KOTOR!