Chiller Outlet Larger than Inlet

[SkyReef]

My Current USA Prime Chiller (1/10 hp) is designed with two different sizes for its water-line inlet and outlet. The chiller-water-line inlet accommodates a 1/2"-diameter line, but the chiller-water-line outlet accommodates a 5/8"-diameter line.

Guessing here, the engineers who designed this chiller had a reason for diameter-size differences between the inlet and outlet to the chiller. I suspect that the design here aims to evacuate water from the chiller with less backpressure (accomplished by a wider-diameter line), as compared to the pressure of water entering the chiller. This design feature probably aims to prolong the life of the chiller and allow faster circulation time.

So here's the question: I am hard-plumbing my chiller lines for the most part. There is no 5/8" PVC in my universe or anywhere, to match the outlet-line's diameter of 5/8". Hence, I must go up or down in size. If I were using flexible hosing, then I could use 5/8"--but that is not a happy choice here because I prefer to hard plumb the chiller lines.

Thus, for the choice of PVC diameter-size (1/2" or 3/4" is the only available sizing relevant here), should I bump up the 5/8" chiller outlet-line to a 3/4" inch line (allowing for less backpressure), or should I scale it down to 1/2" (causing more backpressure on the chiller)?

I think I should go with the larger, 3/4" line--to reduce backpressure. But doing so will release more backpressure than originally designed because 3/4" line is 1/8" larger than 5/8" line.

What do you think? Your thoughts most appreciated. Thanks.