I wish I hadn't looked. But I always do, when I get a PR. I checked the Race Result Predictors at www.marathonguide.com using my most recent 5K and 10K times to calculate what I theoretically *should* be running at longer distances. If I had any endurance, that is.
My 5K time of 30:26 predicts these times for longer distances:
Half Marathon 2:21:20
Hmm, even for my 10K time, I'm nearly a minute slower.
My 10K time of 1:04:31 predicts these times for other distances:
Half Marathon 2:23:03
I'm a long way from going sub-5:00 in a marathon, and it certainly won't be in my next one in January, when I'll have done a half marathon and a 5K the previous day.
But perhaps this tells me that my half marathon PR of 2:38:38 is a "soft" one, that is due for an improvement. We'll see this Saturday when I run the Gar Williams Half in Alexandria, Virginia. The weather report looks promising (40*F and sunny), but the course is rather hilly. It's an informal club race, and I'll be at the back of a pack of fast runners - the last time they ran it the slowest finish time was 2:29! So perhaps I'll be able to push myself more than usual.
I know better than to count on such things, though - PRs are gifts from the race gods and only happen when you least expect it.