3g/4g only lumia 950 xl

[Windows Central Question]

I own a Lumia 640 xl and a Lumia 950 xl both unlocked. The 950 is on the latest release preview ring and the 640 is on a fast ring build of the anniversary update (long time to be updated). Using the same sim card on the 640 I have the option to use 3g or 4g only while on the 950 I can only choose the highest speed (4g,3g,e) is this normal?