"Can anyone tell me what is the largest part LQMT has made (or has had someone else make) to date?"
The problem it doesn't matter what they made in the past since this is a brand new method.
Steipp said the current beta machine at Visser can do up to 7in by 7 inch height/width, but I do recall he mentioned bigger could be accomplished with a different mold.
Secondly, Visser would not be doint the production for any Apple device. Foxconn/Hon Hai would be the producer, they already have a patent published using liquidmetal alloys for both a titanium oxide coating/alloy production process. There is no guarantee they will even use an Engel machine if they have their own method. Remember Apple has the ability to sub-license Liquidmetal Technology patents.
So bottom line is that nobody knows what the capabilities are and if Apple can produce bigger you know they will be tight lipped until its revealed.
-Chris