You can fish the Beach in a big swell but it's not easy. The further out the bank is the better and you will need some big star or similar sinkers to hold you in place. I used to think it was impossible but one night at curl curl I saw a guy get a couple and I matched his tactics with some success. I think there are less fish around but they are still there so u need to spend as much time as possible in the zone rather then drifting through at a rate of knots and then reeling in to re-cast. There's a variety of sinkers for this situation, the pyramids are good as are others with spikes and weight. you may need to use reasonably strong line (18lb )too which may take some of the fun out of fighting the fish and turn it into a skull-drag, but it's more fun than re-rigging constantly because you snapped your line trying to cast the big sinker over 4 feet of shore dump.
I dont think the tide is as important as the general conditions like barometer, wind, light levels and numbers of surfers/swimmers in the water, but I'm still (always)learning. But what you most definitely need is enough water to cover the fish by a couple of feet, some gutters have this at high tide and others at low. Generally on Sydneys northern beaches you can only find enough water at higher tides, lately with all the swell there are some beaches that will actually fish well at low tide byt htis is rare. And finally, I haven't paid any attention to swell periods since I stopped surfing, which relates more to the power of the waves and the comfort of those bobbing up and down on them (boaties) as far as I know than anything tangible for land based fishos - I'd be happy to be proven wrong though!
And one small anecdote from my second outing with the new rod I got for xmas about ten years ago - I convinced my brother in law to fish with me in 2 foot waves, no gutters, onshore wind, almost dead low tide in Janurary (i now know he only came along for the beer) . . . we were running out of servo pilchards because I was so bad at puttting them on ganged hooks they were falling apart, so he changes to the mangled remains from my earlier failures on a single hook and chucks them into the lamest rip running back out to sea and sits back to enjoy his beer whilst I was babbling on like a fool. To cut an already long story short he pulled in a legal Kingie after about a half hour battle on 10 pound mono. having never seen one before we had to get on the net to ID it! I've fished (and surfed) that same strectch of beach semi regilarly for most of my life and I've never seen aother king in the surf there or any other beach.
Cheers,
Gerg.