Here's a site that certainly gets an A for Ambition - Great Science Fiction and Fantasy makes a serious effort to examine the two overlapping genres with a critical eye towards the literary worth of various authors and their output. The site's owner is an interesting mix of ego an anonymity, making his opinions absolutely clear while not even listing his name in any easy place to find. The site is heavy on the verbose and not very easy to navigate, but to his credit, that seems entirely the intention. I don't agree with many of his views, but there are many authors I'd echo on his top 109. Notably absent is Phillip K. Dick and questionably present is Stephen King, but if you look at his very top choices you'll find Tolkein there, so that might give a general idea of where some of the viewpoints are coming from. I would say his site is well worth checking out even if one doesn't measure things by the same yardstick he does, and his general goal of promoting higher literary standards in speculative fiction is a fine one, though his interpretation of high lit may be rather one sided.