For my 5 gal boils I loose less than 1/2 gal over a 60 min boil. Temp is usually around 210 degrees at the top of the wort and that is with a lid covering 80% of the pot.
I then cool, take a gravity reading and add water to bring OG up to what it should be. Been working out pretty good this way.
*** Possum Trot Brewery ***
Beer Primary - $hittyday Stout - Belgian IPA Baby - Silly Scotty Ale
Beer Secondary - Bubbies Belgian Tripel
Bottled - Imperial Coconut Stout - Rotten Red Ale - Bubbies Belgian Tripel - Spiced Scottish Ale - Ovaltine Stout - English Mild - Silly Scotty Ale - A Dirty Dubbell
Mead Primary - Nuttin
Bottled - Strawberry Trainwreck - Orange Spice - Blueberry Trainwreck
2013 Gallons Brewed 80