I have to agree with the fact that a turbo would turn the XF into a short wheelbase lightweight FXO.
But let me tell you about my "old geek" game habits (I am 38) : I mostly play LFS with good ol' friends at lunch break on the corp LAN. We enjoy this marvellous game because it is so close to the fun we have on track days with our real cars. We don't care for more power or this Sauber "game of it's own on wheels" because we do not have the skills, the peripherals and the dedication level of you "hardcore racers". In fact, we see LFS as an extension of our road and track habits. LFS is the only car sim I know where we can race side-by-side for more than a minute without any "the loser will be the winner" algorithmic annoyance. This code is made by guys that KNOW cars, love cars and the pleasures of motor racing (which is part of the english DNA according to my santa pod weekends memories).
Forget about that XF-T, I want my civic -R in that game 8-)