My 20 year old Trek has the original 53/39 chainrings and having the 39t took a bit of getting used to as my other bikes had 52/46 chainrings. If I need a lower gear than I prefer to put an extra large rear sprocket on the cassette. Instead of the 12-25 with normal riding I would replace the 25t with a 28t and if I wanted to go lower I would put on a 34t sprocket and replace the rear detrailluer with a greater range one.
What I love about the gear shift incorporated into the brake levers is that I would not hesitate to switch gears and so did this far more often. Definitely helps in hilly terrain.