I always understood the Norwich in 90 plan relied on upgrading most of the 100mph sections of route to 110mph. But the ordering of 100mph 720's and 755's seems to indicate that is dead. Even though you can achieve the 90 minute timing at 100mph, it probably would have been handy to have the extra 10mph to make up time if needed.
I used the Loco hauled services in from Manningtree for several years during the overlap between Class 86 and 90 and beyond. Even when running to time - we were frequently checked approaching Colchester, and Shenfield. And having a stopper 3 mins ahead at Stratford seems to guarantee a slow-down. Most trains running into termini seem to suffer adverse signals. Liverpool Street is no exception. I wonder if the situation will become more fluid once the Shenfield to Liverpool Street services are diverted through the Crossrail tunnels, allowing the Clacton's etc to use the electric line platforms?