I always fishing on a dropping swell, look at the wave direction. If it is a dominant Southerly swell, dont bother over 1m swell because it seems like its always is bigger. A Northerly swell is ideal with a dropping swell. I always look for 1m or less.
If its to big its just not very enjoyable at birdlings or any of the southern beaches, due to the nature of how the waves break there. but by all means you may be ok with a bigger swell, some people think the fishing is better when its abit rough out there.