I know it's not exactly light, but it is the toughest shell you can get, and IMO the best shell for bushwhacking. The ECWCS goretex parka, you can find them at most military surplus stores and on Ebay. The military has stopped using the woodland camo pattern so you can find the pieces for cheap sometimes as they are being phased out. I bought a brand new parka and pants set for 60$ about 6 months or so ago.
The ECWCS parka and pants are tough as nails, and can stand up to any bushwhacking and ask for more. I ruined 1 nice expensive shell, and will never make that mistake again.
Is it the best shell ever, no. Is it the best for bushwhacking? You bet your ass it is.