with 230 questions to answer in 2 hours & 50 minutes, the expectation (to the best of my knowledge) is that you won't finish the test. i took the subject test straight out of undergrad in 2003 without studying & bombed miserably. took the test this saturday with a minimum of studying, but with the helpful advice to make a first pass through the entire test picking up any & all "easy" points first, then going back & answering questions based on longer passages with which i wasn't immediately familiar on the first pass. i wasn't able to make it all the way through to the end of my second pass before time was called, but i was able to answer 207 questions total, a majority of which i feel pretty confident about. factoring in the 1/4-point deductions for incorrect answers, my guess is that best-case scenario i'll land somewhere in the 80s percentile-wise, worst case scenario i'll maaaaaaaybe hit somewhere around the 60th percentile.
that being said, given that the subject test is so broad (& so heavily skewed away from 20th century literature for the most part (let alone contemporary lit)), depending on your area of focus, most programs really won't rely on the subject test score as any sort of indicator of your potential success in graduate studies. as i've seen others post in other threads, a great score can certainly help your application, but a less-than-stellar score isn't likely to keep you out. the hierarchy of importance re: app materials seems to be (1) writing sample, (2) letters of rec, (3) GPA, & (4) test scores.
also, bear in mind that your SOP (& personal statement if the program(s) to which you're applying have both) is really the chance for you to shine and let AdComm see your personality. it's what sets you apart as an individual. use that. & if you completely bombed the GRE subject test, you can use part of that space to state your case as to why that's not a valid indicator of how you'll perform in their program. the same goes for any aspect of your application package: if you're concerned that it might be held against you & you're confident that it's not representative of your quality of work, let AdComm know. just keep it short, sweet, to the point, & confident as opposed to whiny or arrogant. just my $0.02.