When creating WinPE 2.0 boot images, make sure you run the PEImg /prep command against your boot.wim as it does make a significant difference in sze as shown in the table below:
Bootable ISO file with WiinPE 2.0 Size in MB
boot.wim prepped 146 mb
boot.wim not prepped 203 MB
Considering this all is loaded into memory, you might want to make sure to reduce the size of the boot.wim to an absolute minimum.