Build Advice - GS Duelist

My 73 Slayer (GrndSlm) has finished A10 and started mapping. I mainly use Ground Slam to clear packs and either that or Heavy Strike for single target. I know I need to get better gear, but was waiting for the res penalty before buying/rolling some new stuff. Assume I will get gear decent life rolls and cap res.

I have some decisions to make with the build which I was hoping for some advice on:

* Ground Slam - would the DPS of sunder or earthquake be considerably better? And how much difference would L20/Q20 gems make to either GS or the alternatives?

* Defences - my next few passives will be spent getting the 6th endurance charge. I'm currently stacking armour but would I be better to go for Armour/Evade gear and take some passives like Cloth and Chain for an extra layer? I keep reading about armour dropping off at higher levels, but don't know whether a hybrid approach would just leave me slightly crap at two different things, or if it would actually help

* Blood Magic - using Path of Building I have toyed with taking off BM. I would lose 35% life from tree as a result but then I could run an aura or blasphemy with temp chains/enfeeble much safer, which I guess could be a major DPS boost. I am not far from the Tireless cluster for 20% life and haven't yet rolled or found any decent life jewels, which would go some way to making up the gap

In general, how would you experienced players go about finishing up this tree? Sticking with armour, I would probably go Tireless cluster - Blunt Instrument cluster, and then either Martial Experience for more DPS or Discipline and Training for more life. I could also pick up some stun threshold reduction nodes if they would give me enough of an advantage, or take Vaal Pact which seems to work nicely with ascendancy leech.

Thanks!