Everyone is forgeting the title of this thread.
It is PC superman with ruby of cytorrak against Galactus
and not PC superman against Galactus.
First of all, Cytorrak is well above skyfather level. He has trapped Galactus in his dimension in which he couldn't escape under his own power. Also, if you look at these sites:
http://www.immortalthor.net/marveluniversestats.html
see durability
http://www.immortalthor.net/bio-juggernaut.html
see juggernaut's durability
http://www.immortalthor.net/bio-galactus.html
see galactus' durability
these sites prove that a small trinket of Cytorrak's power can make someone have durability (absolutely indestructible) greater than that of Galactus. Wow! I wonder what is Cytorrak's durability (Or his full power potential). He is probably abstract.
Also, Galactus has stated that he is not very effective against magics.
This is because his science based power doesn't function properly against it. This is why he doesn't like it.
With all that said, Superman (with his cytorrak force field up) will become absolutely indestructible. No radiation can affect him, no being can absorb him, no force can cause damage to him, and no force can resist him (add this to pc superman original force). Thus he cannot lose.
But for him to win is another argument.
This fight is at least a draw for superman.