I don't think I'd wear knee warmers running, either. Too much chance for either chafing or sliding down, and if they don't do either of those, they'll be constricting your thigh muscles. Arm warmers would be fine - even the pros wear them.
If it's a morning race, so you'll be expecting temperatures in the 30s, I don't think lightweight tights would be too warm. They certainly wouldn't be for me, anyway. Over a distance of 5K, the amount of time you'd lose because overheating slowed you down, wouldn't compare to the amount of time you'd spend taking knee warmers off, anyway.
If it's an afternoon/evening race and temps will be in the mid-40s, then shorts are probably okay. You'll be surprised how hot you can get in three miles! Wear some baggy sweatpants or zippered tights - something you can take off without taking your shoes off - and leave them on until just before the start.
Good luck and have fun!
Last edited by OakLeaf; 09-30-2012 at 03:43 PM.
Speed comes from what you put behind you. - Judi Ketteler