You are right about the sleekness. Most Doubles seem to have been built on standard size actions. I have a friend who has a 360#2 that was built on a very slim action by Lang and it is very nice, about 8lbs. Another friend has a Wilkes in 360#2 what is on the same size action as their 470's. 10..5lbs.

My little rifle weighs 7lbs without the scope and 8 with. Check out the pictures of my 450/400 3.25 in the 'Double Rifles Accuracy' thread for a slim and nice rifle.

I have a .577 Thys that weighs 10.5 lbs Light to carry but wales the crap out of you.