This is still RogerDs party and you two can discuss it knowing the universe better than I. I don't like messing with canon(just so things between players can be easier) however if RogerD is confident enough in what he knows to try and whittle down your vessel to the max level in the RP. Basically most the ships in the RP are capable of besting a Star Destroyer, the Victories being the current ones off the line however I'm more along the lines of comparing them to ISDs. However each ship is not capable of taking on more than two of these without sustaining very heavy damage or being blown up.

That is the level everyones ship has to be at. If you two feel confident you can achieve that level, sobeit however in the end it is RogerDs decision. As I said, I know denada about W40k.