a good starting point of flex is that was most of the manufacteurs currently have, thats why you see everytime the same cars in the a-finals in modified and stock.
This cars have a better balance, too. the screw layout is 90% symetric, chassis and topdeck.
You can see this on Fischer's result, with his Serpent he can reach better results. On first training session with his new serpent, he was 0,3sec/lap faster as with his old corally.
I've seen already the new HMX Prototype on track, but it wasn't really fast