Depends. It might help if you are riding on hills. If not, aero is the way to go until the Sora crap out. Then, swap them.

chucksbikes.com had a good deal on 10 speed 105

Doubtful you'll be significantly faster. The extra gears can benefit you, if for instance, you ride 12/25 or 12/27 cassette, then the two gears in the middle will help you find pedal in your sweet spot cadence more efficiently. However, if you're riding a road bike, bank you money and save up for tri bike.

I have an old J-disk (spoked wheel covered with mylar cover) with an eight speed freewheel. I still use it on hilly courses as it is light, and I don't think for a moment about loosing two gears.
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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev