Good question and something I pondered greatly after changing from a CRT RPTV to a 3D LED a year ago. I too now run HDMI through a receiver, mainly to get the 7.1 audio from HDMI instead of having to go the optical route. I do have the cable box with a 2nd HDMI cable direct to the TV and then optical to the receiver for it. That makes it much more wife friendly as she is able to watch cable HD channels without having to use the receiver.
I haven't been able to find concrete measurements of how many ms of lag that a receiver will add, but I did find several settings that seemd to add lag. My receiver isn't the same brand, but let's take the 1000 foot view and generalize on features.
1. Receiver - audio delay. I keep this at 0ms so the receiver doesn't delay either the audio or video.
2. Receiver - HDMI CEC. IMHO I have less lip sync issues on the TV when I shut off the HDMI CEC on both the TV and the receiver.
3. TV - HDMI CEC. Turned it off.
4. TV - input mode - name the input to either "PC" or "Game" (as opposed to Blu-Ray etc)
5. TV - AV mode - also set it to "Game"
6. TV - turn off ALL processing. (120 Hz off. dynamic white off, auto-energy modes off, etc)
HDMI CEC http://elinux.org/CEC_(Consumer_Electronics_Control)_over_HDMI#What_is_HDMI_CEC.3F
The receiver has a win7 PC, Blu-ray player and Game console HDMI connected. Lag was most measurable when using the win7 system and moving the mouse. If the TV's input mode lable is set to "Blu-Ray", I can move the mouse in a circle and take my hand off and then watch the pointer draw a circle on the screen. Setting input mode to "PC" I can draw the circle and not be bothered by it.