How can I reduce the delay when locking the sceen on a MBPr? So with a little research I found that control+shift+fn+power replaces the old control+shift+eject on keyboards without eject keys. However I find I have to hold the keys longer for it to work, probably due to the power button having a delay to prevent accidental sleeping/shutdown.

What I'm looking to do is throw caution to the wind and remove that delay so I can simply hit the key combo not hold it, as I'm more likely to lock my station if it's quick than if I have to do it with purpose.

For reasons related to what system hooks get fired I need to use this method of locking the screen, so other methods aren't what I'm looking for.

It looks like I'll be forking on the NoEjectDelay source to make a NoPowerDelay variation if nothing better comes along.
I use LaunchBar which comes with two actions that are instant: Lock Screen and Start Screen Saver (I have a password lock on resume from screen saver so they're more or less equivalent). Both take effect immediately and because LaunchBar is awesome the commands to remember them aren't some four-key, esoteric, multi-key combination I need to burn in to my memory.

I hit Cmd-Space to bring up LaunchBar. I type loc and I'm on the Lock Screen action. Similarly I can type sta to get to the Start Screen Saver action. I could, if I wanted, make these actions be the top actions for the single letter l and s if I wanted to mess with LaunchBar training, but this suffices.

They kick in instantly.

If you don't want to shell out for LaunchBar (but I tell you it's worth every penny to barely have to touch your mouse in the course of a work day) you can get similar pop-up and actions from Alfred -- it has a lock shortcut you can type to lock your Mac.