I had some problems with too stiff gearbox when it was cold. This time of year we have approx +2celsius in mornings. My clio 200 gearbox was quite stiff and difficult to use before it was warm. I did change ELF NFP oils in gearbox friday. Now it is so much better and gears are easy to change even in morning. When box is warm there is no difference.
2 litres was enough. We had approx 1 meter of tube + funnel, it took approx 5 min to fill 2 litres in box. Really easy & fast way to fill new oil.