By PB 5k was a 20:32 a few weeks ago and based on that pace I decided to try going for a 6:45 pace on the flat parts of an upcoming Turkey Trot 10k, and I did a 5k at 10k goal pace today, and I ended up splitting that 5k in like 20:45, and it didn't feel hard at all. Based on the feel of that I'm thinking about shooting for breaking 1:30 in a half marathon in March.
Now to the points relevant to the title. The 5k was on a little over a month back from taking 3 weeks off from marathon recovery and a minor ankle injury. I had only built back up to 20 mile weeks. In the weeks since then I've hit the 30s, and it running has started to feel more normal again. The 20:32 was also 30 seconds faster than a downhill 5k 3 weeks earlier. So maybe I'm just getting previous fitness that wasn't measured on a 5k built back up.
The shoe part of the equation is that the 20:32 was is fairly beat up Altra Escalates, which are on the lower end of cushioning in terms of Altra shoes. The slightly slower 5k that felt easy was in Puma Nitro Elites, which I know are above my level but $60 more than non super racing shoes didn't feel like that much, and they are a ton of fun to run in even if I don't need them. But could it be the shoes making 6:45 feel easier than it ever has or it is more just getting fitness back up?