Ostrich - belated Congratulations on your 5k PB!
not long now til sub-20... 
my 56-Mile ultra a week and a half ago went reasonably well - it was too hot for my liking for the first 6 hours, I started to perk up as darkness fell, but walked most of the latter half, and finished in 15:42 (yes, 15 hours and 42 minutes)
I feel entitled to rejoin this thread now as:
a) I'm binning ultras for the next few months
b) I'm going to train for a flat 10-Mile PB at a race in November
alright, 10M is still not 5k, but it's the closest you're going to get from me atm! 
my 10M PB is 84mins
I'm sure I can go sub-80, but am going to train towards a 75min target
so, 7:30 miling... 
that's about 4:40/km
yesterday lunchtime I did some km intervals for the first time in over a month
2x2k: 4:49, 4:51 (bit slow, forgotten what to do!
) followed by 4:35, 4:34 (more encouraging
)