Idiots the lot of you!
If the 3 Admirals are the World Governments greatest combat force then surely the 5 Gorosei cannot match or surpass the Three Admirals.
The 3 Admirals would beat the 5 gorosei in a 3v5
I estimate that they're around the Monster Trio's current level, with most of them being Admirals a good 30 years before (except the blonde guy). To be honest they could be a lot weaker than that! The only one I can see being strong is Mahatma Gandhi, none of the others look like strong fighters, they're not even intimidating (except from Gandhi).
They could simply be political geniuses (and therefore appointed to that position), they don't have to be strong to be at the top. E.g. Every countries ruler thus far except from Enel, Hancock and Doflamingo. People like Riku and Cobra are kings, ruling lots of people and yet they're nothing special, Spandam was the coordinator of CP9 and was weaker than a footsoldier!