I ran this at 550 PP (engine upgrades included only engine tuning 3, high rpm turbo, and sports exhaust) and like it a lot. Very quick and nimble, yet easy to control. Good job.
I might turn the brakes up a notch or two and leave ABS at 1, but that's just personal preference. I also tried it without a spoiler because I prefer the look of the stock one, but I did log faster times with a spoiler and downforce of 20 applied as you suggested.