I feel like the skills I have developed in Lit have helped me become better at English, but I still have to work hard at English. It has helped me analyse specific language in greater detail (helpful for Text Response and Language Analysis), but asides from that, doing both haven't really benefited the other.
Not to deter you, but it is really hard to score 40+ in Lit compared to English. You get the top writers in the state doing Lit, but English has people of more varied ability, so if you're a better writer, you're probably more likely to do well in English (not to say you can't do well in Lit). So doing both means you sort of have a back up for your English requirement in your top 4 if you don't do so well in the other. Exam marks in Lit are very unpredictable, so I feel like doing English is a bit of a safety blanket. I wouldn't advise against taking both at once, necessarily. It can be a lot of work doing both at once, but no VCE 3/4 is easy if you want to score highly. Even though Lit was initially frustrating for me at first, I really just tried to enjoy it and it's become one of my favourite subjects.