Is that a legal combo? I was under the impression that it was, but now seems to "either or". I thought one could use Running shot and get the boosted damage from RCE, is this not the case?

RCE specifically says in the PAC that it does not work with other powers, so no, you cannot use them together...

The PAC on Running Shot "This character may use any of his super powers that require a ranged combat action". What else would this relate too?

EE, PW, Incapacitate, Psychic Blast, Muti-shot...