I just try to imagine how big a powerboost a sundipping hour will grant him. I mean...less then 5 minutes sundip had Supes moving planet sized objects...However it all depends on how long Supes can fight under this state.
SBP wins it IMO. I mean...another PC Superman agreed the only way to put an end to Emoboy Prime's rampancy was to smash him through the red sun and take away his powers.
One way for Superman to beat him is to speedblitz the crap out of SBP at the moment he comes out of the sun and have both of themselves smash through the red sun again. Now if this happens there are 3 possible scenarios:
1. They hit the planet completely powerless and Kal-El beats his ass again.
2. Superman's sundip manages to let Kal-El keep his powers longer than SBP.
3. They both float lifelessly in space after their powers are gone.
Under this particular scenario Superman is successful in saving earth from Superboy Prime even if it means losing his life. No big deal...it's Kal-El we're talking about he has been there and he has done that.