Solved

Points or %

Hello, you have to focus on the difference in points, the point gain in research depends on the points you get from the best car in the area you are researching.

The performance you get from adding points isn't linear, the gain tails off as it gets towards the maximum. Adding say 10 points on a low value would be the same as adding 30 on a higher one. With your values given, adding 10 on the 140 will reap a better gain than adding 10 on the 156. 
A balanced car I find performs better as each track has its own criteria for acc, bra, hand, down etc.