You can adjust your gearing ratio by switching the rear cassette. If you have fairly large rings, and no problem going up the terrains you cycle on - but would like to go faster - switch to an overall smaller cassette.

In terms of grade of your componentry I would eschew the Tiagra and opt for at least a 105-Ultegra combo or pure Ultegra. Dura-Ace is top notch gear and probably too pricey. Not only are you saving weight, you also get quality, smoother shifting etc.

I see here Ultegra cassettes coming from 11-23 to 12-27 and you may be better off with a smaller sample.
I understand you are looking into a complete bike, do you have links?
are you looking into 9x, 10x, ??