I am currently using Valiant F16H and it has 600HP engine. It goes at a maximum speed of 90-95 km/h. I am thinking of upgrading the engine to 750HP. Would it be beneficial?
As you probably guessed, you don't get a benefit to your maximum speed, as you'd be speeding if you went any faster than this. (Well, you can go faster, but you really shouldn't.)
But, you do get better acceleration and the ability to keep your speed up when going uphill. Depending how heavy (or light) loads you have been pulling thus far, you may not have noticed a need for these yet. But once you get to the heavier loads, you'll notice the benefits of upping your acceleration and being able to maintain your speed when driving uphill.