For me the whole point of going carbon is to go light, and 1700g isn't a light wheel in my opinion. I don't really notice a big difference between in braking performance between carbon and alloy rims on flats and shallow descents. I guess I feel more confident descending with alloy wheels but honestly I have a tough time slowing down on steep descents using rim brakes regardless of rim type. I also try not to ride in wet weather.