Your'e getting the slow from polar station which means no spitfire which means less efficiency from ballistics. Not sure if worth it. There's a fire m6 build with chemical burns that works out pretty well but only in a team where you already have someone providing you with slow / chill and even then, if that team member dies you lose cotw damage bonus which is quite huge.
At higher BPs using impale leads to your sentries shuting regular bolts again(using a 3 spender setup). In terms of aoe ea/fa > impale by far. Since you are using a "rocket build" changing spit fire to polar station is again a huge hit in e-dps. To have a rough idea which skill setup performs better for your current gear just plug in your numbers at http://d3profile.com/ and see how different spender setups perform.
84m (Impale+CA+MS) vs 94m (CA+MS+EA) w/o wolf buffs for sure.. Ye EA with spitfire turrets look's better. Thanks for the d3profile link