(19 Feb 2016, 3:28 pm)GX03 SVC wrote Northallerton is 125mph according to Wikipedia when I last looked.
Yep - I think the speed limit is 125mph without any changes from just north of York to about 1/4 way from Darlington (may be wrong).
As for Thirsk, The platforms are in a 'loop' style with the fast lines running in between the two platforms.