There really isn't that much difference in size/weight between the 3.5-10 Leup and the 3-9 Conquest.....the Leupold
looks trimmer, though.
I like Dober's suggestion of a 6X on a light mountain rifle....unless a guy is totally "variable dependent"...
That said my pal has a 3.5-10 on his Mashburn and that is a pretty light rifle consideing the caliber. It sure won't break you down on a mountain.