I often find it helps to announce goals to other people, it makes it seem more real and more concrete. It also helps put a *twinge* of pressure on you, though honestly that's the last thing I need!!
D - Anything faster than last years 4:53. Worst case, I still want to beat last years time.
C - 4:30. This time is totally doable. My incredibly hilly, tough 21 miler last weekend was about on pace for this. That would also give me a 20+ minute PR. Wait, and that's only my C goal???
B - 4:20-4:30 This would make me really happy. Very realistic. Possible 30 min PR? Oh yes, I'll take it.
A+ - Sub 4:20. My first 20 miler was amazing, and it set me up for a time around 4:18. According to my half marathon PR set just a few weeks ago, McMillan pegs me at 4:20. It is not a crazy pace for me (9:58) but I know I cannot afford to slow down too much towards the end. I need to force myself to NOT WALK just because I'm tired. Of course I will be tired. But I need to shuffle my little legs towards victory. This is the time I really, really, really, REALLY am striving for.