Best of luck with Clarissa. One of my daughters is named Clarissa, though I've only read extracts from the novel. I was once on a badly planned course on the 18th century novel in which students were given a week to read Clarissa. Needless to say, no one succeeded. Fielding's Tom Jones, half the length of Clarissa, was more within my grasp and I've read it twice.
My wife staggered through volume after volume of Proust in English translation, but still didn't reach the end.
At university I got through a big chunk of Gibbon's Decline and Fall of the Roman Empire. The prose style was magnificent.
It took me many months to read Boswell's Life of Johnson, although it's not a particularly long book. I kept by my bedside and it was a great sleep inducer. A paragraph acted like a blow to the head with a blunt instrument :-)