I ride the same bike, rain, shine, summer, winter - a cheap Giant OCR4 road bike. I used to ride a hybrid before someone nicked it from my garden... A road bike is undoubtably quicker when up to speed. However, I find that the steering is sharper on flat bars. In summary, unless roads are fairly car-free and without traffic lights, you'll always be able to gain more through filtering than through absolute top-end speed.
Well that's my observation, anyway.