Interesting speed comparison A345 vs A380
 

Just watching outbound traffic and noticed the Etihad A345 @ FL340 416kts and behind it the Singapore A380 @ FL350 doing 416kts so there doesn't appear to be much difference in speed at that stage of the journey. However earlier in the climb process the A380 was significantly faster than the A345 and did appear visually to gain ground on the A345 during the climbout phase.

Speed comparison
 

I assume 416kts is an industry/company policy-dictated speed rather than an a/c capability constraint, or is it an Airbus-designed optimal cruise speed?

It may be I wasn't saying that 416kts was all they could manage however it was clear the A380 gained considerable ground during climbout over the preceeding A345.

I realised that but 416 kts is not just a co-incidence so I'm curious why they were both travelling at that exact speed at different FLs in different aircraft - was it ATC direction, fuel consumption optimisation, company policy, or something else?

Well there are other aircraft at that altitude which were traveling considerably faster so It could be some sort of SOP of maybe just coincidence. Unfortunately I can't track them further than that last position so I can't tell if they were assigned higher cruise altitude (I think they would have) and what their ultimate cruise speed was (dependant on cost index?). However inbound aircraft (international) were over 500kts (All around 520kts).

All domestic aircraft however had cruise speeds around the 450-470kts mark.

If only we had someone west of the mountains with a SBS receiver we would get some great coverage.

Everyone knows A340s only climb but for the curvature of the earth! :D

But seriously, don't forget the A345 - the heaviest of the A340s - is going non-stop to Abu Dhabi - twice as far as Singapore - and is therefore loaded to the gunwalls with fuel.

I naturally assume the A346 was the heaviest?

Nick,

Take a look at this little comparison tool offered by Airbus you just need to select which aircraft type you want to compare.

Grant great link!!

Interesting the A346 sacrifices fuel for increased volumetric payload whereas the A345 sacrifices payload for fuel. The A345 does in fact have a higher MTOW (4 tonnes heavier).

Both aircraft would have been flying a Mach number generated by on-board computer systems designed to minimise fuel burn. This speed varies with altitude/weight/wind etc.
The resultant ground speeds would be coincidental (there must have been some headwind involved for the speeds to be that low), but would indicate the two aircraft have similar cruise profiles.