I have an elite lvl50 summoner. My skill tree looks similar to this, but if I were allowed a respec, I would make it exactly like this.
http://hellgate.ingame.de/skilltree/summoner/?l=50&s=1700830000002100001800050300Everything gets put to 8/10, 5/7 and 3/5 because of the 2 master's hand I'm using, which add +1 Summoner skills each. Elementals don't do nearly enough damage to kill anything in act5/endgame in elite nm, so I highly suggest going with a warper build instead of a carnagor one. The force elementals tank perfectly fine, and with 4 of them you can be sure that you'll have at least 1 out at all times. With this build you have 10 extra skill points to play around with, so there are some optional skills you can go with.
+1 in Word of Fear if you find yourself having to run away from mobs too often, it the only "escape skill" available to you.
+3 Elemental Drain (takes another 5 just in pre-requisites) this is what I chose to spend my extra points in on my summoner. In Elite NM while killing the 5 lies and syd, elemental drain helped a huge amount, allowing my fire elementals to ingnite a few times.
+more in summoning circle - Don't max this out to 8/10, but instead find 2 weapons which add 2-3 to summoning circle/+to warper, and use them while summoning instead. The life boost will stay when you switch back to you main weapons.
Don't put any points into reaper, just get a weapon on switch that adds to it. I use him in emergencies when all my warper gets overwhelmed. He works as an emergency skill instead of word of fear.