
My thoughts exactly...
OP: the Mk IV Cobra was absolutely panned by just about everyone for not being a Cobra III, cheat mode. I like the big girl, I think the compromises work well, but I'm in the minority. I suspect your combat Cobras would face a similar reaction- the Cobra's speed and versatility are well balanced by it's size. If you want something bigger and harder hitting, FD will take away something else to compensate and balance the new ship. That balancing probably wouldn't go down particularly well with the majority of the player base.
Good luck with your suggestions, I'd buy both if they were ever made available, but don't get your hopes up for them entering the game, or being dramatically better than anything in their class even if they do.