I got the Xi3s and I am happy with them. I think there is still a small loss of efficiency with them, but it is hard to say exactly how much because the temperature usually changes significantly at around the same time the tires get changed. There is a massive difference in traction in cold, snowy conditions though. The OEM tires are awful in the snow, even when compared to other all seasons.
I went with 205/60R16, as they are a better match than 205/55R16 to the diameter of the stock 215/50R17. I also prefer the bigger sidewalls when the potholes start to appear in the early spring. Ideally I would like to use 205/60R16 in summer and 195/70R15 in winter, but 15 inch wheels won't fit and it isn't worth changing the 17 inch wheels the car came with.