So here's the recap clothing wise and race wise: Start temp was 23, finish temp 26. Winds generally light between 5-10. Went with shorts and wind briefs, long sleeve tee, thin stocking cap, and fairly thick running gloves. Had a short sleeve over the long sleeve that I threw off at about mile 3.
Adverse affects from the cold: fingers on left hand numb from mile 15 on due to wind direction and various spilled Gatorade and water. Toes lost quite a bit of feeling at about mile 15 as we'll, felt like club feet. Probably mainly mental effects but still annoying. Legs and body were fine.
Had originally targeted breaking 3 hours at Des Moines but had some piriformis issues (self diagnosis, but traditional treatments helped), so punted to tulsa. Course was hilly, lots of turns, never on a groove, and obviously cold. Went through half in 1:31 and finished in 3:06, with a numb left hand and numb toes.
Wore hyperspeed 5's instead of nb1600's after seeing the course, with hills, turns, quite a bit of concrete and torn up asphalt for more cushioning. Absolutely love the hyperspeeds but you don't need the ventilation they provide when the temperature is in the mid 20's.