Well, to get you audio and stuff setup, yeah just
1. Click the AppleTV Preset
2. Video Tab switch from ABR To Constant Quality and set the slider to 68%
3. Advanced Tab Paste that string:
bframes=6:ref=6:mixed-refs=1:subq=6:me=umh:no-fast-pskip=1:trellis=1:weightb=1:bime=1:brdo=1:direct=auto:vbv-maxrate=4900:vbv-bufsize=3500
into the text field instead of the old AppleTV string (tabbing out of that text field will cause the correcsponding widgets to reflect the string state).
You are now good to go. Go have a drink, get a sandwich or read a book (like war and peace) cause if you think the stock AppleTV preset was slow, this is slower yet to encode.

Seriously though, I just set 'em up before going to bed and let it go over night. Thing is, constant quality will vary bitrate according to the source and what x264 needs to maintain that visual quality. So some movies might end up at 2500 abr when they are done, some might only be 1800 and some could be 4000, you dont really know for sure. Though typically I see somewhere in the mid 2000's. Again, try it and see if you like it. I am not saying it is for everyone, but its where most of us at HB who use atv's have been at.
As well, remember if you like that setting for yourself, just save it as a preset so you don't have to go through the steps every time. You can of course always set it to be your default preset (just like any of the rest of them) so HB automatically loads it up at launch. Good Luck