If you already have 3/4 inch valves, stick with them. Most pros only use 1 inch valves, regardless of the pipe size, in order to simplify their inventory. That reasoning would apply to their only using 1 inch pipe, as well, regardless of flow.
If there is a surplus or deficiency in the sprinkler pressure, you should be able to compensate for it by changing the nozzles, once you've seen the as-designed performance.
