Hopefully this will help with some of the differences in the 80x's:
GWR 800/802 - no real difference as both classes now have same rated engines and work in multiple together. The 802's have roof mounted brake resistors.
LNER 800/801 - 800's have 750 rather than 940BPH engines, 801's have a 'limp home' engine also have mini buffets.
TPE/Hull Trains 802 - smaller kitchen, assume same as the 5 car GWR otherwise.
Lumo 803 - electric with no 'limp home' engine and standard class only.
Avanti 805/807 - believe has a different engine to the earlier 80x series on the 805, mini buffet and smaller kitchen. 807 - electric with no 'limp home' engine and new length of 7 coaches.
EMR 810 - 24m so can fit a 10 car set into London St Pancras.