Another advantage to a low delta T, 5/8 pipe or 3/4 pipe is that on a space of this size the value of a condensing boiler or Geo loops starts to add up as delivered water temps can be held low. in the 100 degree range. The small additional cost of pipe combined with reduced manifold cost and on going fuel savings start to add up.
Dan

return water temp is the cause of mod/con savings. supply temp, not so much. High dt design is better for modcon efficiency as long as you don't break MFG spec for allowable dts.

with geo you can't do as high of a dt, definitely, because supply temp is more important. cases like that 5/8" might make more sense to accommodate higher flow rates. but you can almost always do a 30 dt in a commercial space with 100 degree water temps or less and since I don't usually order 1000 foot 3/4" rolls the "less loop" argument is kind of moot. uncovered slabs are pretty good emitters for sure. You can do some great stuff with them.

and even accounting for the marginal output improvement of 3/4" over 5/8" is a bit ambitious I would say. I doubt there is a heat load calculation in existence on a commercial building prior to a slab pour that is accurate enough to design to that resolution.