Running

I tried to get a 10k pb at lunch, but missed out by 10 seconds, which was frustrating. My 10k pb pace (43.34) significantly lags my 5k pb pace (20.08). How can I carry the pace over distance better? More endurance stuff? Note, this is off relatively light, unstructured training. I find time for about 40km in a good week and 20km in a bad week.

try doing some k reps, measured on somewhere you know.
if you can keep to sub 4.00 mins, then try and do 8 of them smoothly.
in a real 10 k race you will be buzzing with adrenalin at the start,
able to bang out some extra at end, so concentrating on 8 good smooth ones= sub 40, 10k
(its my aim too, got 19.03 5k but really want to rinse this in may)