@ EniGmA
You'll want to save up more than 738k for upgrades easily. I would say keep your 599 and grind more cash, and more importantly respect points, in the Face to Face races. These should be very winnable with a well set up 599. Trust me, its so much easier to make money with a highly tuned not so good car than an untuned high level car.
Go for something in the region of $3m and 3000 respect points if you can, before upgrading.
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How are people doing in the Pro League?
Got a Lambo doing quite nicely in level 6, hard to get below 8.95 for the 1/4 mile though. Anyone having any fine tuning tips? cheers