Well, you don't actually get to choose the vehicle speed, unless you can choose the engine size too
Most vehicles are way overpowered in terms of optimal efficiency. I suppose it is possible to detune the engine too, hadn't really thought about it.
But assuming you have complete control of the gear ratio for cruising and can hold the target rpm, the load (of which aerodynamic load is no small part) and the velocity are dependent. If you make aerodynamic improvements you will be going even faster for a given engine load after the appropriate gear ratio adjustment. And thus could also downsize the engine to keep the previous cruising speed.
I don't know what the best acceleration gears are except that you can have too few and to many. The shifts shouldn't be so far apart that you are forced far from the "sweet spot" rpm wise, but not so numerous that you spend more time shifting than accelerating.