Yo, just joined and thought I needed to share something.
I beat the story mode a week after the game came out, and have been screwin around ever since. Today I decided to get to 100% for shits and giggles. The first thing I did was fly under the 14 bridges and got that achievement, 40 Gamerpoints and it probably took me 20 minutes. Then I did the stunt jumps, which took me about 5-8 hours. I had a printout from here, checking off all the ones I had done and shit, and the achievement for that was only 30 Gamerpoints.
I guess what I felt I needed to share was...thats !@#$ing retarded. Anybody else feel that's a bit off? Seeing that, I'm scared to see what kind of "reward" you get for beating the game 100%.