i immediately fell in love with dostoevsky's work (just finished my third read of TBK), but it took me a long time to get into david foster wallace - now, i think of them as very similar. DFW is known for a lot of things (long books, footnotes on footnotes, early death) but to me at the end of the day both infinite jest and the pale king (his posthumous novel) are both incredible works that ultimately deal with existentialism. what made me think of them esp. is your comparison of C&P (cynical) and the Idiot (optimistic).

to me, infinite jest is the cynical but fun work (it's about a lot, but it's a lot about how people use drugs and entertainment and tennis(!) to (unsuccessfully) distract themselves from their larger existential problems), and pale king is the optimistic but more serious work (but with a strange reason for optimism, built in large part around the transcendence of being able to tolerate crazy boredom - it's a post-modern book about IRS employees for heaven's sake. there's a good dose of "we should probably be better citizens" - one of my fave sections describes how US taxpayers view themselves as "consumers of the government" vs. "participating citizens", digs really deep)

i actually like pale king slightly more even tho it's posthumous. it's also shorter (500 vs. 1000), i'd highly recommend starting there, though since you did TBK first, maybe you can just jump into infinite jest no problem =)