I have a feint memory of someone here posting that the OLE on the MML being reinforced in order that EMT (now EMR) trains could run at 125mph where the line speed allows. This had been started by replacing the most troublesome headspans south of St Albans.Yes. (copy GWML and ECML practice)
The older lower tension systems run into contact wire oscillation issues at lower speeds than (modern) higher wire tension systems. min 75m pan spacing with modern B+W pantograph and older OHLE will get you to 100mph (sometimes 110mph) but above that you have to make changes.
Greater the distance between pans reduces issues and higher wire tension reduces issues.
the 804 configuration will give about 198.5m spacing but only 102.5 or 120m depending on unit orientation if they were positioned mid-unit.
I could be wrong of course.