Runway heading 34L/Right turn: Blame the Q. ATC can do this where traffic complexity dictates, although with simultaneous fanned turboprop/jet departures of 34R it becomes pretty tricky unless you can maintain the 34L departure at 4000'. Q said they can't maintain 4000' on departure except in emergency. When Nth American departures require the right turn, ATC will normally hold all 34R departures until the 34L is 10 miles upwind. Great efficiency gain? Directanywhere - there's also a Terry Hills resident affected by these departures, but I think he likes jet noise. An upcoming airspace redesign is in the works and this may improve the situation, but it is primarily designed for relaxing requirements on arrivals to the expense of "screwing" the departures... something Q was quite happy with.
250kts: for jets departing in the "wrong" direction (eg 34L for the SE, 16R for the NW), best rate of climb is needed to get to 10,000' above the inbounds. Apart from that, high speed is normally not a problem. For arrivals, blame Q. With all their jets doin' economy 265kts, the whole lane slows down.
Frink hit the nail on the head... the odd inefficient departure is nothing compared to legislated LTOP delays. Write to your local member
Movement rate: With the number of heavies at SYD, I reckon it would be hard to get to 100/hr. I think 90ish was achieved once or twice (the limit is the metered rate, not the actual rate). Some limitations include ATS procedures which restrict the arrival spacing to 5NM in the 34 direction, 4NM in the 16 direction, to get a departure in every arrival gap. There are efficiencies to be gained here with correct technologies. LTOP restrictions on the use of 34R/16L often cause much greater delays on 34L/16R than would otherwise be the case. Also, blame the Q... seems to be more and more of their crews "requiring" the long runway with over 15kts xw, blowing out the system-wide delays. What's the deal?
Bottom line, SYD is constrained by local residents and their political representatives. Damn democracy, don't you hate when it gets in the way of good business? I'm sure a quiet word into the ear of Macquarie will get their attention. Either that, or jack up the surcharges on the punters, and call it a "Sydney Noise Abatement Surcharge".