@axavierhansz: Or it's possible that Majin Vegeta in his SSJ form was equivalent to Vegeta in his normal SSJ2 form. Then when he powered up to fight Vegeta he became SSJ2 Majin Vegeta, which let him match up to Goku's power level.
But it seems that the key difference between us is the gap between Goku and Vegeta. I believe that Goku was far beyond Vegeta, which is why Vegeta needed the added bonus to even match up to Goku whereas you seem to think that there was less of a gap between the two and the Majin transformation doesn't grant a significant power boost?
Either way lets leave this debate here, I see that I can't convince you and you haven't really convinced me either. Let whoever can be bothered to read our debate come up with their own conclusion as to how much of a power boost the Majin transformation gave to Vegeta.