Repulsion Bomb or Temp Invulner

Im doing a respec on my fire/energy blaster and Im trying to deside on whether to take Repulsion Bomb or Temp Invul. My build is light on AoE since I wont be taking Flame Breath (took Blazing Bolt for the snipe instead) and only really have Fireball as my AoE. I have Temp Invul in my current build but other than in teams (with enough endurance buffs) and against elite bosses/AVs I dont wind up using it much. Against elites its stacked with FoN to pretty much cap me at S/L resistance. So Im wondering if Repulsion Bomb is good enough to skip Temp Invul. PFF and FoN are the two powers that are a must have for me.

I think you'd be better of with Ice Mastery. It doesn't take much effort to cap S/L defense with Snow Armor.

However, if you're dead set on Primal Mastery I'd go with Temp Inv. Unless you want to get some sort of bonuses out of Repulsion Bomb that is.

I was thinking the Repulsion bomb a bit more for teams and dealing with the packs of multiple minions (an area where my build is lacking). I was thinking the knockdown effect should provide a desent amount of mitigation as the mobs struggle to get up. Was thinking of this pattern Aim+Buildup+Repulsion Bomb+Fireball when soloing.

As far as Ice goes as an epic pool I tried it on one of my other blasters and wasnt superbly impressed but I may give it another shot on him since he is already fire/ice. This toon however I definately want to keep Force as my epic pool since he is designed to a degree around killing elites/AVs and FoN is invaluable for that (particularly when soloing them). Plus fire/energy is about pure power and doesn't provide much cc (other than Total Focus) so the extra survivability from PFF and FoN I have grown to rely on.

The end cost for such a low amount of mitigation would put me off of repulsion.

I have Repulsion Bomb on my Fire/Elec, and really wish that you could use it first and not get immediate retaliation before the mobs are knocked up. If it worked so that you could use it as a safe opener, it'd be so much better.

Blazing Bolt takes out one even-con minion in approx. five seconds.

Fireball/Fire breath takes out an entire spawn of even-con minions in approx. five seconds.

I know, I'm "Stop having fun!"guy, but that's why I make the choice I make... and why every nonfire blaster I have makes me wish I was driving a fire blaster instead.