Looking at this picture we learn something about speeds of various ships:
the Deux-Sevres in the small fleet is going 13642 KM/s and has a thermal of a nice round number; 2000
the Deux Sevres in the big fleet (Red 2) is going 13608 (not quite 13642) and has a thermal of not quite 2000 (1995)
yes , as you may have guessed 13608 is 99.75% (1995/2000) of 13642.
If we assume that they have engines that have a thermal of 1000 and ships with 2 of them. (because the Marengo went from 2000 thermal to 1000 and went to exactly half speed when hit)
then we can figure out that the large fleet is moving at the maximum speed of 13608 and is limited by the ships with a thermal of the nice round number:
the VOSGES! not the Sarthe! The Sarthe has a thermal of 3938 It is the FASTEST of these ships! it should be able to go 13822 KM/s !!
The others have a maximum speed of very close to the 13608 that they are currently going:
Lot-et-Garonne 5999 13,610 km/s
Gard 3998 13,615 km/s
Sarthe 3938 13,822 km/s
Vosges 2000 13,608 km/s
Deux-Sevres 1995 13,642 km/s
So not only do we know which ships are slowing them down, we know that the speed difference between their ships is very small, and more importantly:
OUR GUNSHIPS ARE NOTICABLY FASTER!!!!!!!
No guarantees (the ships at 3998 thermal might have 5 or 6 engines instead of 4, letting them be much MUCH faster), but that's the way to bet.