Per-minute average spread on my raw account:
- 07:45–07:59: 0.30 pips
- 08:00–08:05: 0.55 pips, with spikes to 1.2
- 08:05–08:30: 0.25 pips
- 08:30–09:00: 0.20 pips
All-in cost for a trade in the calm part (after 08:05) came to about 0.9 pips including commission. So for a 5-pip target, cost is around 18% of the target. On EURUSD in the same window, I get closer to 14%.
My conclusion: AUDUSD at London open is tradeable but not great. It's fine as a second pair when the Aussie has its own story, such as a strong Asia move or Chinese data, but I wouldn't make it the main London pair.
If anyone has numbers from a different broker, please post them. Curious whether the 08:00 spike looks similar elsewhere.