Little Lightning
Ski Diva Extraordinaire
I did a quick comparison between the 2 bikes. The differences in the 2 bikes would be 11 speed vs. 10 speed and Shimano 105 components vs. Tiagra components. 11 speed appears to be the current industry standard. 10 speed was high end 11 years ago when I built my bike.
Shimano 105 components are probably lighter in weight and more durable than Tiagra. We used advise friends in the market for a bike not to go lower than 105 components. The lineup of Shimano components are Dura Ace, Ultrega, Shimano 105, Tiagra, Sora and Claris. Shimano 105 is right in the middle between high end and low end.
Sounds like you're headed in the right direction and can now make some good decisions.
Here's a discussion of Shimano components. Scroll through the comments section for a 2016 review of the different versions of components. https://www.evanscycles.com/coffeestop/advice/shimano-road-groupsets-the-hierarchy