In my experience, nothing you write in the LFM posting will truly filter anyone. The harshest, most cruel LFM advertisement you can possibly think of will still attract clueless players who don't even read what quest your doing, they just notice it's a highlighted lfm in their level range.
However, I can say that writing a stern lfm posting will usually deter more casual players from wanting to group with you, as their first impression after reading your lfm is your an a-hole.
People enjoy the game on various levels. some players dont care about deaths, dont care about exp per min, heck some even dont care about getting to cap. You can't really divide the playerbase into two simple groups as there are players on all varieties of play skills between the best and worst players.
tl;dr - This is the internet. Have a thick skin and if making an elitist LFM bugs you, then suck it up an deal with more casual players joining your group and ruining your play experience - just keep in mind, if someone dies and leaves, it is most likely due to embarassment, not intentional sabotage.