I have used an 8wt for largemouth bass, but after seeing them attack 6" bluegills at the pond, I have considered the possibility of using a 10 wt. Some baitcast anglers are tossing 10" worms for trophy bass!
I used a 20 lb "saltwater" leader on my 8wt. Sometimes I believed that leader was too light...I would drag 10 lbs of weeds with a 2 lb bass inside! I wouldn't feel "overgunned" with a 40 lb leader, should I need to pull a double digit bass out of the salad!
I've pulled my share of LM bass with a 4wt. When they hit the weeds, I normally wade to the weeds, slide my fingers down the line, grab the belly and mouth, and claim my prize!
My next "bass" rod may be a 10wt...sometimes bass like something big to eat! Tossing Jitterbug sized poppers sounds fantastic...hooking the bass that hits that popper sounds even better!