Rough numbers.......very rough.......would result in about 0 savings  per acre.

if 200 x 200 = 40,000 sq ft......that is almost an acre.........43560.

If run a line every 30 ft...........that is about 200 / 30 = 6.67 lines.  (Count the side pieces how you want-------- still is ABOUT 6.67 lines.)
each line would be 200 ft long.
200 x 6.67 = 1334 ft.

If run a line every 40 ft...........that is about 200 / 40 = 5.00 lines.  (Count the side pieces how you want-------- still is ABOUT 5.00 lines.)
each line would be 200 ft long.
200 x 5.00 = 1000 ft.

If 3. inch tile were .30..........and 4. were .395........
3 inch tile ........30 x 1334 = 400.
4 inch tile ...... 39.5 x 1000 = 395.

The carrying capacity of the 3 inch is 1.5 x 1.5 x 3.1414 = 7.07
The carrying capacity of the 4 inch is 2.0 x 2.0  x 3.1414 = 12.57

So..........the question for me is one of which would stay the cleanest.  Looks like the 3. would..........same water thru more constricted tube..........given the application is one where a lot of water is not likely.

So.......for applications like sidehills, where the runs would be long, but probably not have to carry as much water since the surface would drain a ton of water off before soaking to the tile.................then the question is--------- would the 3 inch likely retain less silt etc than the 4 inch?

Or...........is the probable difference so small that one need to not worry about it?