I will check my settings in Beersmith and report back. This may be a dumb question - Doing extract and partial mash even I never really considered efficiency since adding LME/DME usually got me to within a point or two of my anticipated OG, but now that it looks like it is important how do I calculate it?
Regarding grain crush: I want to believe my LHBS guy is pretty good, but I could see him milling the grain incorrectly. I wasn't there when he did it. I usually e-mail my order in and pick it up on my way home from work. Will definately look into this more.
I have a high tech wooden volume stick I made, so I will have to remember to measure my post-boil volume and grain absorptions as well next time out, but I think 5.5 gallons is a good estimate. Fermenter was at the 5 gal mark, and there was some left in the kettle with hop trub and break material.
You are correct, there is a set amount of fermentables in LME/DME and there's not much you can do except to screw up your volumes to mess that one up.
There are many, many variables to efficiency. If you can stand some nerdery, try taking a look at Kai's take on it: http://www.braukaiser.com/wiki/index.php?title=Understanding_Efficiency
For something a little less in depth, try this one: http://www.howtobrew.com/section2/chapter12-5.html
Another quick point about wheat malt is that the kernels can be a smaller size that malted barley. You may need to have it milled twice at the LHBS to get a good crush on their setting.