8 rounds will be enough if the circumstances of the shooting dictate that it will be enough. It's not possible to accurately say more than that.
However, it is possible to point out some things that will have absolutely no effect on whether 8 rounds is enough or not.
1. The shooter's preference in self-defense handguns. Liking revolvers or pocket pistols--even liking them a LOT--won't mean that the amount of ammunition in them is always sufficient to prevail in a self-defense encounter. There's no way what a shooter likes or prefers can possibly dictate the circumstances of a shooting such that it limits the number of rounds required to the number of rounds in the shooter's gun.
2. Whether or not the defender can reload quickly. Not even if the defender can reload as quickly with a revolver as an autopistol. If a reload is required to finish the encounter then 8 rounds was clearly not enough.
3. What gives the defender peace of mind. Being comfortable with the amount of ammo in the gun will have absolutely no effect on the circumstance of the shooting a defender is dealt. I know people who are comfortable with carrying no gun at all. A defender's comfort level won't preclude him from being in a shootout that calls for more rounds than his defense gun holds.
4. What the defender has used to adequately protect himself/herself in the past. There can be no guarantee that the next encounter will be like the last one.
5. Rationalizations provided to justify behavior or decisions already made for other reasons. People are amazingly adept at rationalizing the decisions they've already made or behavior that they've already chosen to engage in. Reasons provided as rationalization for the decision to carry a low-capacity defense handgun will not change the outcome or circumstances of a self-defense encounter. For example: John decides to carry a pocket pistol because it very conveniently fits in his pocket easily and doesn't poke him like a larger pistol carried in an IWB does. His ability to come up with other reasons to justify/rationalize his decision won't have any effect on whether or not the capacity of the pistol will actually be sufficient for the self-defense encounters he will be faced with.
I'm sure there are more, but that's a good start.