In a round about way, yes, you will gain more water at your sprinkler heads. Using larger diameter pipes decreases pressure loss. You can't gain more volume than what your house can supply, but you can increase dynamic pressure by using larger pipes.
Rule of Thumb: Do not exceed flow for the following PVC Pipe Diameters
3/4"......<12GPM
1".........<20GPM
1 1/4"....<35GPM
Note...Poly pipe has different limits.
Based on your 16GPM zone, you are losing roughly 6psi in that 60' stretch of mainline. Compare that to 2.5psi lost if it were 1" PVC. Keep in mind, your 1/2" laterals are where you're losing alot of pressure.
I don't understand why people switch lateral size. Keep it all one size. Saves time and limits the number of repair parts needed.
This post has been edited 2 times, last edit by "Central Irrigation" (May 28th 2012, 3:07pm)