RE: What large EDF unit makes the most thrust?
There are many different 120mm EDF systems on the market now. They range in price, quality, and assembly. One example is the [link=http://www.xtremepowersystems.net/products.php?cat=33]Dynamax Xtreme PRO 2 fan system[/link] from XPS. They also sell a mating nacelle if you want to hide the DF unit.
Extreme R/C in Australia has a series of [link=http://www.extremerc.com.au/estore/index.php?main_page=index&cPath=146_72_298_301]120mm EDF[/link] units.
Park RC Models distributes the RC Lander [link=http://parkrcmodels.com/product_info.php?cPath=33&products_id=1003]120mm Dynamic Power Series Metal EDF[/link] unit.
Good luck!