Motor control signal resolution
OK, 1-5 hp motors is something I work with on daily basis. As I said in the comment, the smoothness is subjective. Here are my subjective observations.

At this power level the load driven usually has enough inertia (e.g. scooter weighting around 200kg with the driver) to make motion smooth enough even at 60 steps resolution. However the noise level from the motor has distinct steps too, which makes 60 perceived as uncomfortable. For this reason we usually have at least 1000 steps of resolution.

Now, the most questionable part of your design is the use of DAC. There is nothing wrong with analog power stage. In fact, it can give you infinite resolution and very smooth motion. However you are limiting that with DAC, and not only resolution-wise, but also slow (relatively) response time. Discrete PID implementation has strong dependency on time constant, and your fastest loop time will be limited by communication speed.

So, if using DAC is not absolutely necessary for your design I would strongly suggest using PWM output to power stage. It will simplify your schematics and PID will be easier to tune up.