A gear ratio of 4.8 is essentially the same as 53:11 = 4.82, i. e. overkill even for most fit road cyclists, much less a gravel bike.
I’m not sure how you relate gearing to speed, but you can easily reach 50 km/h with 1x gearing and a moderate chain ring size. I have a 42-tooth chainring on my road bike (1x), and I can pedal up until 60–65km/h. On the (false) flats, when I am able to go about 50 km/h (about 30 mph), I’m not in my top gear, but previously in 50:13 and now in 42:11 spinning at a comfortable 100 rpm.
Both, 1x and 2x work fine, it is simply a matter of preference at this point. The main question is what lowest gear you need, which depends on the terrain as well as the ratio of gravel to tarmac.