As mentioned above, there are folks who can gut it out and finish a 50 miler on a base of 25 miles per week.

 

There are lots of other folks who wouldn't attempt a 50 miler on less than 80 or 90 miles per week over the previous 3 months.

 

I've been actually toying with the idea of attempting a 50 miler on a very easy course this April and am leaning toward not running it.  I'm sitting on a base of about 50 miles per week right now and plan on ramping that up to 60 mpw training for a 50K in April.

 

I've started daydreaming of signing up for the 50 miler instead of the 50K, but think that is probably a bad idea.  With my base I think a 50K would be almost an enjoyable race on an easy course.  I'm afraid the 50 miler would become a death march for those miles from the mid 30's to the early 40's.

 

You do more trail running than I do though and if you are used to pacing yourself and mixing in lots of walking then you might be able to pull off the 50 miler without too much pain and suffering.

Run it. I am guessing the worst thing is you will probably be sore for a week.