I went as far as I could go in the 50 years of 911 without doing any upgrades or spending any gold. Here is what I was able to do.
1. Bought four of the 911´s (two you could only buy with gold so I passed and 1 was free)
2. I was able to complete 72% of the game (Update Now 75%)
3. My R$ total dropped only 144k*. (Update now 128k)
4. My Gold Increased 19. (Update Now 35)
5. I placed first in all but 6 that I raced. (Update now 4)
I still could put in a little upgrading and get the 75% bonus which would increase my gold another 16. I decided not to my the gold cars in hopes that someday they would appear with a 50% discount. (Update, reached 75% with no upgrading)
* The 4 911´s I bought were with the 20% unlocking discount. You need to have the R$ in hand before you begin so that you can take advantage of the discount.
Here where my results:
72% (Update 75%)
26 1st Place (Update 28)
1 2nd Place
3 3rd Place (Update now 2)
1 4th Place (update now none)
1 8th Place
9 that I was unable to race (2 were for PR Limit)