Wish I had seen this sooner.
After my first respec for my PB, I went Nova/Dwarf having learned the hard way that being jack-of-all-trades doesn't work so well. Now, I'd have to say he's one of the best blasters and tanks in a given group.
I did go with Health/Stamina/Hasten. I toggle those on (along with the HP boost, Conserve Energy and Build Up) before entering Dwarf form and rush any Voids or Quantums, usually knocking them down long enough for the energy blasters or the scrappers to help take him down before he can kill me. Sometimes, he's even dazed. Hit 'em hard and fast seems to work for me.
For my 2nd respec, I did take the level 35 primary "nuke" power. I think I'm disappointed with it. While it could be a good 'oh, shoot!' power to save fellow team members in trouble, it's often suicidal. Just not worth the debt. When I have a blue insp, I will click that and go into dwarf form quickly. Sometimes that works, sometimes it's 'the floor tastes funny' time.
So, I'm looking at respec #3 unless I can think of a good strategy to use this power. So far, no luck.
Oh, one another recommendation for the teaming Kheldian: don't slot knock-back. It disperses the enemies which really ticks of the blasters, trollers and defenders with AoE powers. I find they get knocked off their feet plenty and knocking them back 10+ feet only means I have to run around a lot.
The exception to the above is the Photons. Though I don't slot their knockback either, it tends to send them flying anyway. If all three hit one enemy though, it's usually just a ranged attack to finish them off.