Having a career race leaderboard can be both good and bad. On the good side it shows you how you did compared to your friends on the bad side it prompts you to use an over powered car which make the races themselves less interesting.
Forza 2 had this and most of us liked it. I did every race in career mode at least twice in order to improve my overall rankings. They removed this as of Forza 3 and added a lot more races and a race calendar so to speak at which point I found the career races pointless and ran less than 1/2 of them. on Forza 4 I probably ran less than 10% of them for the same general reasons. To many boring races, no leaderboard on them, no prize cars, no fun. Better to just race online and totally ignore the career after Forza 2.
I enjoyed career mode in GT6. I went through every race and only found myself bored on one race SSX like the wind, just mindlessly driving fast in a straight line is not very interesting. Fortunately it was just one race and only took a few minutes. All the others were fine.
A leader board for these would be cool but a hot lap leaderboard would be much better