I don't think they'd be mispronounced, no more so than most names (plenty of names get mispronounced and it's no big deal -
Sara,
Ada,
Eva,
Caroline,
Alicia,
Madeline for examples). Both are pretty intuitive, and easy to correct if it happens.
Definitely prefer
Portia.
Porcia has a porky thing that's hard to shake. I read somewhere that
William Shakespeare changed the spelling of
Porcia to
Portia specifically to combat the piggyness, and wow am I glad it stuck.