Hm, I would think Death Spores should be really nasty against symbionts, but it could be the opposite, the healing of the symbiont might provide resistance.
Still, OR is really tough too, so... my money's on OR.
Colossus is stronger than Omega Red. Yet Red managed to subdue Colossus with his tentacles rather easily. So strength goes out the window. Speed: Carnage is faster than Red and as I have said before, Carnage could manage to slice Red's head off by slashing at Red's neck.
The question is can Carnage do that?
What if the entire Carnage symbiote were to enter Red's body through his nostrils or ears and completely destroy his body within?