Saying that, if GNE were to drop the X9 and just have the X10, I would suggest looking at a full fleet evaluation of the E400MMCs & Volvo B5TLs. The major deciding factor would be the evening & Sunday interworking patterns at Consett. But, if it would be feasible to adjust the interworking patterns:

Service changes
X30/X31 (PVR 5)- Revised to operate standalone from X70/X71/X72 during at least Monday to Saturday daytimes. Revised timetable with more recovery and layover time at both ends of the route.

X70/X71/X72 (PVR 7)- Revised to operate standalone from X30/X31 during at least Monday to Saturday daytimes. Revised timetable with more recovery and layover time.

ADL E400MMC
6336-37 - Consett - Spare
6338-42 - Consett - X30/X31
6343-51 - Chester Le Street - X21
6352-55 - Riverside - X10 (IF X9 is dropped and PVR reduces to 4x)

Volvo B5TL
6308-14 - Consett - X70/X71/X72
6334-35 - Consett - Spare

Wright StreetDeck
6331 - Consett - X45/X46 (stays at Consett)
6332 - Consett - Spare (stays at Consett)
6333 - Chester Le Street - Spare
6377 - Riverside - Spare