Setting up a skill tree for MF Culler

I haven't been down the road before of creating a culler for farming purposes, so I was curious how to approach the final product. I've spent the last few days racing a build through all the levels up to act 4 in Merciless - I could have pulled up once I got to Sceptre of God but figured I might as well chase the extra passive from Indomitable Spirit. The build is at level 43, so I'll spend the next day or so doing ledge or whatever to build it up to the 60's so it can take on board all the necessary MF gear.

Question is, given that the build's sole function will be for putting in the kill at the end of farming runs, shouldn't I just respec all the attack passives I've used to progress and simply throw everything at defense just for the occasional situation where it might need it? Seems kind of pointless to keep the dps up when the build's chief function is to apply instantaneous death via the Culling skill.