When loading the WINPE boot image with PXE from your distribution point, you might be able to speed up the boot time by increasing the TFTP block size.
In my test scenario the boot time was one minute faster after the change, and this is often a part of the OSD installation where we are actively waiting, so faster boot time are more than welcome.
On the Distribution point with PXE support find the registry key HKEY_LOCAL_MACHINESOFTWAREMicrosoftSMSDP
Create a new DWORD value RamDiskTFTPBlockSize and use the values 4096, 8192 or 16384 depending on what gives you the best performance in tests.
Start with the value 16384 decimal.
After changing/adding the value restart Windows Deployment Services Server.
And then test to see if the boot time is faster.
Please note that you might find older hardware that wont work with larger TFTP block sizes, so test carefully.