I'm reading Manuel Quieroz's excellent new book 'Chasing the Morning Sun' about his transworld trip in an RV6. He took both sat phone and HF, and found the sat phone useless in the air. I believe he felt the mic did not cope well with cockpit noise, maybe other reasons too.
The HF worked well. Manuel strung the long HF aerial wire along the port wing and then onto the tail, and he found it caused a significant out-of-balance trim, requiring slight pressure for hour after hour on the rudder (his Pacific flights were around 15 hours). He used each foot in turn and occasionally both feet!