One reason I know I'm fretting about half-marathon pace and times is that I am (pointlessly; procrastinatorily!) thinking ahead to my first marathon in November.
Like many runners, I obsess about arbitrary times that end with zeroes!
(Hmmm, should convert everything into someone's wayward eighteenth-century or science-fictional decimal time system and shake up those expectations...)
And it is a feasible hybrid of optimism and realism to think that I might be able to go just-sub:4:00 in a flat marathon on a cool day. 3:58, that's the aspirational goal, leaves a bit of wiggle room (because I do not like really having to worry about splits to the second, not enjoyable to me).
But really on current speeds 4:10 or 4:15 might be a more appropriate goal for the first one--this is just a note to myself not to mess up my chance at a really enjoyable and evenly paced first marathon by going for an unrealistic time goal. I think I need to have done a couple half-marathons quite comfortably in the low 1:50s before 4:00 becomes realistic--in fact maybe sub-1:50 would be the more conservative test.
The Grete's Great Gallop half is the one I'll do six weeks or so before the marathon, but that's on a quite hilly course and Philadelphia is very flat, so lowish 1:50s would be fair, I think (sub-1:53:00, maybe, given hill differential?)--MacMillan associates 1:53:48 half-marathon time with 4:00 marathon, but I have the impression a lot of experienced runners find those predictions over-optimistic, especially for beginners doing relatively low mileage.
If I train sensibly and don't get injured, it seems to me still possible that this will be both an appropriate and attainable goal. But I will have to wait and see. Thinking partly prompted by some interesting mulling-over of my times in the NYRR database. (I think this link will work.)
I had an anomalously fast half-marathon in Philadelphia in November that's not represented here, but it's rather striking to me otherwise that though each race seemed to present its own set of issues (for instance, for the October one I had a great taper that left me feeling incredibly lively and well-rested, but it was evilly hot and humid), and the courses are not equal in difficulty, I have a very steady albeit modest improvement on mile pace: 9:10 in August, 9:05 in October, 8:57 in January, 8:54 in February. The last race was by far the easiest of the four, in every respect--flattest course, appropriate weather (barring wind issues!), no illness or exhaustion issues--but clearly I really have become a faster and better distance runner in the last six months.
Re: marathon goals, though, I can see (feel!) that it really does take experience racing at a particular distance before one gets comfortable at that distance...