Well thank you very much for all your answers!
Concerning the 1- (about V-gears), I guess this has something to do with the shape of the gears in the mechanical transmission, right? Or is it an initial?
This is a case, when there is hydraulic (Dr14, Dv12) or electric (Dr13) transmission, which has selectable speed/TE range. Consider it as high gear and low gear.
Basically, selecting V-gear (of Dr14 locomotive) activates a part of transmission which provides maximum tractive effort (269 kN), but with lower speed (43 km/h) than the top speed (75 km/h). Normally there is a T-gear selected and that provides 180 kN of tractive effort, with mentioned 75 km/h top speed. V means "Vaihtotyö", which means shunting (use), and T means "Tavara", which means freight (use).
Actually, i do not know if it's a physical flip-swich switchable gear or other part on transmission which changes the speed and traction effort.
There is similar gears (T and M) on Dr13 and Dv12 locomotives.
Dv12 has normally M-gear selected and that provides 125 km/h top speed with 142 kN of tractive effort, and T-gear can be selected, providing 85 km/h top speed with 200 kN of tractive effort.
Dr13 has normally M-gear selected and that provides 140 km/h top speed with 210 kN of tractive effort, and T-gear can be selected, providing 100 km/h top speed with 290 kN of tractive effort.
In addition of previously mentioned T-gear, M-gear means "Matkustaja", which means passenger (use). All these gears (of Dr14, Dr13 and Dv12 locomotives) can be selected by refitting, and are compatible with all livery options.
In addition of those (in real life train driver selectable) gears, there is also some other speed-related refits available:
-Some of the newer Sr1's had 160 km/h gearing instead of normal 140 km/h gearing (that couldn't be simply selected by throwing a T/M- or V/T-switch like on Diesels). That can be also set by refit after certain date, and is compatible with livery options. Tractive effort drops at the same scale when speed increases, at normal gear 140 km/h 280 kN, and 160 km/h 244 kN.
-There is an Dm7 transmission refit available after certain date. Some later units had 5-speed gearbox, Wilson R11B, which provided 115 km/h maximum speed, and refit replicates that. By default Dm7's have 4-speed Wilson R11A gearbox, which provides 95 km/h maximum speed. Tractive effort remains the same with both transmissions, and all livery options are available as well. DmG7 has same refit available, with same specs.
-Dm10 had 120 km/h top speed at first, but later it was dropped to 100 km/h after it was discovered to have too bad brakes for 120 km/h running. 120 km/h top speed can be still refitted if you dare. Tractive effort remains the same in both cases.