When I'm playing as France I start research on 1939 infantry at least a year ahead of time without any speed boost.
With the 50% bonus from NF, I start work on 1940 fighters some time in 1938. It's really nice having RADAR and some Dewoitine D520s when the Germans come knocking with Bf109s, but as you can imagine i struggle not to fall behind in other areas, with France only having 3 tech teams (the 4th tech slot arrives fairly late in 1938 such are the demands on the NF tree to get rid of France's nerfs, and the 5th, due to distractions such as the army that got within sight of Moscow showing up on your doorstep.