I agree that some other routes could possibly benefit.

But Percy Main's B9TLs are not only overkill for their current work (307/309), but also in VERY good condition considering their age.

If the Angel StreetDecks end up on the 307/309, you'd have something like


StreetDeck:
- 6301-03 - Washington
Spare (x3)

- 6304-07 - Percy Main
Spare (x4)

- 6315-29 - Percy Main
307/309 (x15 if 309 PVR increases)

- 6330-33 - Washington
34 (x3)
Spare (x1)

- 6356-76 - Washington
14/50/X1 (x21)


B9TL:
- 6043-44 - Consett
Spare (x2)

- 6045-48 - Various depots
Spares 

- 6086-6108 - Consett
16/16A/47/X5/X15/X45 (x23)

- 6109-17 - Riverside
X21 (x8)
Spare (x1)


B5TL:
- 6308-14
X20 (x3)
Spare (x4)


E400MMC:
- 6336-51 - Consett
X30/X31/X32 (x5)
X70/X71/X73 (x7)
Spare (x4)

- 6378-91 (TBC)- Deptford
56 (x14)


That all means for decker frontline work:
- Consett = E400MMC or B9TL
- Washington = StreetDeck
- Percy Main = StreetDeck
- Deptford = E400MMC or B5TL
- Riverside = B9TL, E400, E400MMC, EV (TBC)

A hell of a lot more simple too. Consett's issues pretty much sorted and E400MMC can be prioritised on the X30s and X70s. No voyager, ex-London, ex-Tyne Tees Xpress or GAG tat doing frontline work for the most part. The Durham Diamond E400's could have some use on the Gateshead local work.

Percy Main practically all StreetLite and StreetDeck. Deptford have enough decker spares - I doubt GNE will order a spare E400MMC.

All the 20/70 plate StreetDecks kept together at Washington and trusty B9TLs doing the X21.

Also, got to take into account that at the moment, GNE are using heavy duty B9TLs on planned 353/4/5/6 workings - StreetDecks will not only save a lot more fuel on the 307/309, but will also save fuel especially on any Nexus secured trips or trips interworking off the 307/309.

And for brownie points, I'm sure NECA would support more efficient StreetDecks operating on a corridor with known high levels of pollution.