Black Templar assault termies with lightning claws are pretty mean dudes. I prefer to dispense with thunder hammers entirely though. I want all my hits going at once with these guys. None of that powerfist-thunder hammer swinging last stuff. This way my squad can tear through enemies quickly and brutally. Since termies in their codex still can buy veteran skills I give them furious charge. Being Templars they get to be fearless in an assault. And being in terminator armor makes righteous zeal more fun. I've always interpreted the 25 percent casualties as meaning any wound counts. I assume this means you don't have to fail a saving throw for it to count. Any wound saved or not counts. So being in that nice armor means they can be shot and likely survive. And then pissed off and go all righteous zeal towards the nearest enemy. Even if a lose a couple the lightning claws, tough armor, and sheer meanness of my Templars ensures they'll mangle whoever they assault. And if my vow is Accept Any Challenge, No Matter the Odds it makes them even nastier.
As for popping tanks I have plenty of other ways to that. I have another squad of shooty termies. Between the assault cannon, cyclone missile launcher, powefists and chain fists they can kill a tank. Or one of my other units will do it. Leaving my assault fellows free to mince troops.