go for a road bike. there’s only one place to put your hands on a flatbar as opposed to a road bike. you’ll be glad you have the options of changing hand positions. don’t think i’d want to ride 70-80 mi on a flatbar bike no matter how skinny the tires are. thin tires with high pressure increases speed but they don’t keep your hands from numbing.
Or you can put on Trekking Bars & have as many hand positions as a road bike bar. One the plus side, the Trekking bar also keeps you more upright and gives you greater visiability than the road bike handle bars. I upgraded my mountain bike bars for a Trekking bar for $20