How much of a difference would shifting from a (24/34/44, 14x28) to a (28/38/48, 11x34) configuration make when going downhill? I currently have a Proton MTB with a 24/34/44 crankset and a 14-28 cassette. I have found the configuration to be lacking when going downhill: The front chain ring doesn't feel stiff enough on the highest gear resulting in me pedaling too hard.

How much of a difference would it make if I shift to a 28/38/48 crankset and a 11-34 cassette? This configuration is found on the Giant Roam 3 (2018) which I am considering buying. I've done some math:

On the MTB, running the highest gear, I am at an effective gear ratio of 44/14 = 3.14 while the Roam 3's config would give me 48/11 = 4.36. On paper, this is a 38% increase, but I am not experienced enough to know if this translates to a significant difference when pedaling.



The other configuration I've mentioned is actually on another bike that I am considering buying (Giant Roam 3 2018). I am not looking to modify the current bike.
38% is a huge difference, and very noticeable on road. Since the bike you are considering has 622mm rims, it adds even more to the effective gear ratio.