I absolutely love my Perf Koenigsegg but you must increase the weight otherwise it's too light to hold traction at high speeds and performs worse than stock. You can hit 230mph at a push (274mph is my highest on road) but the acceleration is where it's unparalleled. Street races are a dream because you just power away after taking each corner.
In addition, I like how Ivory Tower crafted these unique attributes to each part such as extra grip/speed/braking/etc to allow you to build any car into the specific style you require. Trouble is, you need to farm multiples of high level parts.
It's details like this which allow fine tuning rather than simply getting a car to level 1299.