I purchased the 2.1 and am about 1500 miles in on this bike. I ride as hard as i can and it shifts perfect every time. I see no real downside between the 105 and the tiagra shifters. So i saved the cash, gave up 1 speed on the rear and have had no complaints. I dont see the 2.3 being worth that much more than the 2.1. I would expect more for my $500+ price difference.