actually there is something similar to the "b-spec" since the first forza.
in the first forza this mode was way more complex than nowdays. Im talking about more options and devlopment of your own hired driver, it was kinda fun to train your driver and it was like +1 thing in the game. let me give one example about what i remember of it. by selecting a driver to hire, you could notice a few diferent locations ffrom driver´s nationality and also displays the amount of cash that he would ask for race to you, also hes "lvl" of ability in diferent things like "cornering,overtaking and etc". i remember this from forza 1 also. lets say you choose one driver, a low lvl driver. you would have to train him. im not sure if i remember the right modes that would allow to train him if there was a "test race" or something specific. but you had 2 options:
1 you drive alone on the track, doing your best and every thing that you do counts for in some specific skill that you would be training for the driver. like... chicanes, U-turn, and a bunch of other skills. Lets say you was on track training him, and you are great on chicanes for example...each time you passed by a chicane the driver would recieve an amount of XP points for the "chicane" skill and so on. making he driving like you drive each time you train him.
In Forza 2. there was not a such detalied training for your driver...i think they cut it 80% of that what i explain about FM1. to hire a driver you only need to go to any race, and instead of choose the option "race" you look down on menu and there was an option "hire a driver".....in FM2 "hire a driver" features:
-choose hes nationality and ficticious names
-there was only a "master lvl" (like lvl 1,2,3.... of your driver). No more training him in specific things
-by the lvl of the driver he would charge more for racing ( if you choose the best driver on the list, it was like 75% of the racing money)
and just that for the forza2
in forza3 and 4 it remains like Fm2, with some little changes, but, still the same basic thing....choose you car like you would race. choose your race, and instead of race you hire the driver
sorry but im not sure yet about if is possible to raise a driver skill in Fm4, but soon as i see i report here