So, there is my findings:
1. WinXP SP3 x86 and win2k3 SP1 x86 processes startup items in different order.
2. None of startup items is processed in Safe Mode.
3. Nor WinXP SP3 x86 nor win2k3 SP1 x86 processes any RunOnceEx.
4. The only synchronous is HKLM\RunOnce.
5. HKLM\RunOnce is processed first -> nor desktop items nor TaskBar is yet shown.
This patch by Edijs Kolesnikovičs fallows win2k3 SP1 x86 procession order.