I think this is one of those questions that everyone can have an opinion on, but noone can truely answer. There are an awful lot of variables:
- How many attackers?
- How close are they? cover?
- What are they armed with?
- How big/fat/tough/angry?
- How good is your shooting at that moment?
- Where are you able to hit him/them?
You will only know the answers to those questions after the incident, if and when it happens.
With the 5 shot revolver you described, if you are (somehow) able to shoot very well at that moment, I'll bet you can take down two guys. On the other hand, from the anecdotes I've heard, and FBI stats I've read, few people shoot well at this sort of time. For example, recently on another thread someone described taking on a small black bear (190lb) with a revolver, I had the impression face to face distance - he emptied the 5-shot revolver, and only got two hits, one of which was in the foot - not trying to criticize, this seems to be common.
While I'm sure the 5-shot can do it with cool marksmanship, it wouldn't hurt to have a few more round. I am a full-sized handgun guy, so I don't really look at that end of the scale, but I believe that a well designed compact 9mm can hold more rounds than a comparably sized revolver.