@peternlewis, as I understand it, you use AppleScript to implement many of the Keyboard Maestro elements. If so, would you mind sharing the AppleScript for Running Applications collection.
It runs very fast.
Here's my test macro for those that might be interested:
tell application "System Events"
set appNameList to (name of every process where background only is false)
end tell
set AppleScript's text item delimiters to linefeed
return appNameList as text