Hawkeye will actually be pretty usefull in act 6. His sp1 drains power, and you'll NEED that for 6.1 Infamous iron man is good for act 6 from all that I know (never played him). Valk is top 3-5 skill, depends on who you ask, so definitely keep her. I find BWCV a little overrated but she's usefull. Ultron is hecka good too. Save up your 5* shards and use them on the science mystic duel crystal and hope for Magik or Scorp. And if you got torch he's really good for 5.4.5 mephisito. For 5.4.3-6 I had to use a couple revives to get through, it's not too bad. Wait till you hit 6.1