Booked 8-car services in the peaks (other than where you would expect to find them - eg Rainham, Sutton Loop, Sevenoaks, Orpington, GN non-core services) are I think the following from diagrams posted online - some of the Rainham services start at Bedford as, in order to use Bedford Carriage Sidings effectively, the units have to work Rainham or Sutton Loop services.
Southbound
0443 Bedford to Brighton (0549 St Pancras)
0515 Bedford to Brighton (0619 St Pancras)
0548 Bedford to Brighton (0649 St Pancras)
0634 Bedford to East Grinstead (0724 St Pancras)
0852 Bedford to Three Bridges (0939 St Pancras)
1535 Bedford to Gatwick Airport (1651 London Bridge)
1602 Bedford to Gatwick Airport (1721 London Bridge)
1635 Bedford to Gatwick Airport (1751 London Bridge)
1746 Bedford to Brighton (1905 London Bridge)
Northbound
0622 Brighton to Bedford (0723 London Bridge)
0759 Brighton to Bedford (0904 London Bridge)
0828 Brighton to Bedford (0934 London Bridge)
0845 East Grinstead to Bedford (0940 London Bridge)
1533 Gatwick Airport to Bedford (1636 St Pancras)
1603 Gatwick Airport to Bedford (1706 St Pancras)
1803 Gatwick Airport to Bedford (1906 St Pancras)
1833 Gatwick Airport to Bedford (1936 St Pancras)
Seems fairly obvious how they have planned this.
Looking at open data sites, it looks like there are some changes to the 8-car workings on the Bedford to Brighton / Gatwick Airport / East Grinstead routes associated with Bedford Carriage Sidings from May. I make it that the following are 8-car:
Southbound
0443 Bedford to Brighton (0549 St Pancras)
0515 Bedford to Brighton (0619 St Pancras)
0548 Bedford to Brighton (0649 St Pancras)
0634 Bedford to East Grinstead (0724 St Pancras)
0846 Bedford to Three Bridges (0939 St Pancras)
1519 Bedford to Brighton (1635 London Bridge)
1549 Luton to East Grinstead (1641 London Bridge)
1535 Bedford to Gatwick Airport (1651 London Bridge)
1548 Bedford to Brighton (1705 London Bridge)
1746 Bedford to Brighton (1905 London Bridge)
Northbound
0613 East Grinstead to Bedford (0704 London Bridge)
0622 Brighton to Bedford (0723 London Bridge)
0800 Brighton to Bedford (0903 London Bridge)
0830 Brighton to Bedford (0933 London Bridge)
0845 East Grinstead to Bedford (0940 London Bridge)
1533 Gatwick Airport to Bedford (1636 St Pancras)
1603 Gatwick Airport to Bedford (1706 St Pancras)
1751 East Grinstead to Bedford (1856 St Pancras)
1803 Gatwick Airport to Bedford (1906 St Pancras)
1758 Brighton to Bedford (1921 St Pancras)
1828 Brighton to Bedford (1951 St Pancras)
I have traced them as being the following diagrams:
A
5W13 0258 Bedford C S to Bedford
9W13 0310 Bedford to Brighton
9T04 0622 Brighton to Bedford
9T93 0846 Bedford to Three Bridges
5T93 1036 Three Bridges to Three Bridges Tl Up Depot
5R90 1548 Three Bridges Tl Up Depot to Gatwick Airport
9R90 1603 Gatwick Airport to Bedford
5R90 1802 Bedford to Bedford North Sidings
5R91 1927 Bedford North Sidings to Bedford C S
5T67 2038 Bedford C S to Bedford
9T67 2049 Bedford to Brighton
9W18 2324 Brighton to Bedford
5W18 0224 Bedford to Bedford C S
B
5T05 0446 Bedford C S to Bedford (via Bedford North Sidings)
9T05 0515 Bedford to Brighton
9T10 0800 Brighton to Bedford
9R19 1035 Bedford to Gatwick Airport
9R34 1303 Gatwick Airport to Bedford
9T45 1519 Bedford to Brighton
9T96 1758 Brighton to Bedford
9R59 2032 Bedford to Gatwick Airport
5R59 2247 Gatwick Airport to Three Bridges Tl Up Depot
C
5T07 0532 Bedford C S to Bedford
9T07 0548 Bedford to Brighton
9T12 0830 Brighton to Bedford
5U12 1052 Bedford to Bedford Cauldwell Depot
5L89 1526 Bedford Cauldwell Depot to Luton
9L89 1549 Luton to East Grinstead
9L22 1751 East Grinstead to Bedford
9T65 2018 Bedford to Brighton
9W16 2256 Brighton to Bedford
5W16 0144 Bedford to Bedford C S
D
5W05 0102 Bedford C S to Bedford
9W05 0115 Bedford to Three Bridges
9W14 0415 Three Bridges to Bedford
9L85 0634 Bedford to East Grinstead
9L12 0845 East Grinstead to Bedford
5L12 1058 Bedford to Bedford C S (via Bedford North Sidings)
5T47 1536 Bedford C S to Bedford
9T47 1548 Bedford to Brighton
9T98 1828 Brighton to Bedford
5R63 2048 Bedford to Bedford (via Bedford North Sidings)
9R63 2135 Bedford to Three Bridges
5R63 2353 Three Bridges to Three Bridges Tilgate Sdgs
E
5L02 0444 Three Bridges Tilgate Sdgs to East Grinstead
9L02 0613 East Grinstead to Bedford
9R11 0832 Bedford to Gatwick Airport
9R26 1103 Gatwick Airport to Bedford
5R26 1314 Bedford to Bedford C S
5R39 1522 Bedford C S to Bedford
9R39 1535 Bedford to Gatwick Airport
9R54 1803 Gatwick Airport to Bedford
5J55 2015 Bedford to Cricklewood South Sidings
At present a further 8-car working is out and back from Three Bridges depot in the evening peak having sat out most of the morning peak - presumably this will remain in place.
5W06 0206 Three Bridges Tl Up Depot to Three Bridges
9W06 0215 Three Bridges to Bedford
9T03 0443 Bedford to Brighton
5T03 0730 Brighton to Brighton Down Siding
5T96 0938 Brighton Down Siding to Three Bridges Tl Up Depot
5R44 1518 Three Bridges Tl Up Depot to Gatwick Airport
9R44 1533 Gatwick Airport to Bedford
9T55 1746 Bedford to Brighton
9T60 2025 Brighton to Bedford
9W19 2305 Bedford to Three Bridges
5W19 0136 Three Bridges to Three Bridges Tl Up Depot
Finally, the balancing working to diagram B is:
5W05 0450 Three Bridges Tl Up Depot to London Blackfriars
which goes on to work a Sevenoaks diagram
Clearly, it is important for there to be some 8-car workings on these routes to get units back to Three Bridges depot for maintenance but difficult to keep them away from peak workings.