If you're serious about your running performance and comfort, you should seriously consider the Arc'teryx Women's Cita 3/4 Tights. Arc'teryx crafted these tights out of several ultralight fabric panels for a fine-tuned, tailored fit, with smooth seams and built-in mesh vents for extra comfort. The tights weigh in at a mere 180 grams (which is about as lightweight as tights can ever hope to get). And since the tights' Altavela stretch fabric dries in a flash and draws moisture away as you perspire, you can stay cool, calm, and collected with your eye on the prize. (I.e., being first to cross that finish line.)
I love this pant. I was looking for a flexible, breathable pant to climb in and do yoga in. I was also hoping the pants would be good for biking in the spring. These pants are perfect. They fit well, they breathe, they stretch nicely without feeling like I need to adjust them, and they come below the knee (great for rock climbing when I forget to drop knee). If you are looking for something similar, buy 'em.