Ric is spot on. I own a high-racer (Challenge Seiran), and the steering took some getting used to. Now I commute 25 miles to work (each way), including about 8 miles in traffic, and have no problems. For serious mountain climbing, particularly over 8 degree grades, I have to keep my speed up (4mph or better) in order to avoid "wobble" that can lead to heal strike -- easier said than done if I'm tired.
For best speed, a low-racer with full fairing is probably the way to go. I've thought of getting a rear fairing (sock type) for better speed and visibility on my high racer, but there's too much gunk on the road these days.