I am a little bit concerned about Borg cubes. They would either be way too small to be a threat – they would be only slightly bigger than the Vengeance. Vengeance is so huge and sinister that Borg cubes won't look as ominous now.
When did Spock try to save Romulus? Because Voyager already returned from the Delta Quadrant with 'trans-phasic torpedo' technology as well as that special shielding that Spock prime would be aware of.
The Borg are already defeated by Spock Prime's future knowledge.