Having gone from Arch Ex’s to Flow Ex’s, I much prefer the Flow’s for the added support and volume they give to big tyres. The weight difference is not great, but it is noticeable.
The two rims seem virtually identical in design except for the width. I do have trouble believing that the extra few mm of width lends a noticeable amount of stiffness to the wheel itself. I’d be interested to hear anyones opinion on that though.