I just bought a Sandisk 16gb UHS-1 card from Bestbuy locally and did some unscientific (using a stopwatch) random testing multiple times and can confirm the writing speed increase is super beneficial.
X100 Raw file write Class 10 32gb Centon card: 2.9 seconds
X100 Raw file write Class 10 16gb Sandisk UHS-1 90mb/s: 1.8 seconds
XP1 Raw file write class 10 32gb Centon card: 4.3 seconds
XP1 Raw file write class 10 16gb Sandisk UHS-1 90mb/s: 1.9 seconds
Don't even need a timer or care to, it's just faster and very useful.. I think even the light blinks faster.