I think it was 2007 when I got in the National 50 with a 2:21 or something, was seeded last or close to it! It was on the F1/50 or some variation of it, I think I did a 1:53 in the end and fancy going back as I reckon it would be alright for fixed, even the lumpy bit at the southern end.
I scraped in with a 2:09 a few years ago when it was on the P885, but if it's not on a fast course pretty much any time will get you a ride in the 50.