I shot weddings in the past, and yeah, this can be a problem. You do not state what camera you have, but my solution with my Canon was the 70-200 2.8 L lens with image stabilization, (IS). With the addition of the IS, I felt that made up for any extra speed I would have with a faster prime lens, yet I still had my zoom when needed.
I am pretty sure Nikon has a similar lens if that is what you are using. So bottom line, a zoom with 2.8 can work well if it also has image stabilization. That lens is NOT cheap though.
Actually, if you can afford the fast IS zoom, you should also be able to afford a fast prime, something in the 1.6 or 1.8 range is much less expensive than the 1.4, and you are only talking about four tenths of a stop... sometimes you have to look beyond the numbers and think in practical terms of what that tiny amount of extra speed is really worth in dollars and cents.
So, if your budget is very limited, get a fast prime, in most cases you can use your two legs as a zoom. If your budget is larger, get the fast IS zoom AND the prime.
steve