737-700ER speed

I don't think anyone has brought up this question yet but why does the 737-700ER/winglet fly at 840km/h but the 737-700HGW/winglet fly at 850km/h? Shouldn't they have the same cruising speed?

I don't have any technical data to back me up but it is just from a logical point of view. All wingletted 737s fly at 850 except the -700ER.


It says .785 Mach (at 35,000 Feet), That is the same as the other members of the 737-700 Group. Hope this helps!

Nevermind just saw something. deleted