Soldato
the truth of it is that the frame, the fork, the wheels and the contact points make faaaaar more difference to the overall experience than the difference between 1 groupset and the one above or below it.
While it's true that they're often overlooked, the groupset is very important. The difference between thumb shifters (think Tourney is the only one still manufactured) and STI is quite big for the ability to shift in the drops. Microshift/suntour will get the job done, Claris and Sora will do the same but maybe feel a bit smoother to shift. From what i gather there's not really much between the two, or even Tiagra in terms of shift speed or feel, it's just the number of gears. 105 and up is supposed to feel a lot better, but when you get to that price you also have to consider SRAM which a lot of people prefer for doubletap, it's just a shame that so few bikes actually come with it.