Have been wearing a Fenix 3 (non-HR) for two years now as my daily wear watch. I love the size and don't even notice the weight of the watch. I run daily and don't even think about the watch on my arm anymore. I like the "big look" of the F3 and the wide 26mm strap... So from this standpoint the physical size of the F5x doesn't concern me at all (only 1.5mm thicker - no big deal).
According to all reviews and specs per Garmin, the F5x (w/ silicone band) is 16grams heavier than F3 and 12g heavier than F3HR. I know that its not in the wild yet, and my question is speculative as only those at CES had a chance to try it on, but I wonder if this size increase is noticeable? Wondering if it might begin to approach a weight that starts to really push the limit of comfort for an active but also daily wearing watch?