Charts like that are what cause oversizing. That is hose size which is based on fluid velocity AND its ultra conservative. My new L3901 with LA525 loader and a 6.3 GPM system uses -06 hoses straight from the factory. The grapple I purchased arrived with very high end Parker -04 hose and -08 Stucchi flat face couplers,- ARRRRRG!!!!Looking at charts like this: https://clearwaterhydraulics.com/hose-size-vs-gpm-ezp-24.html -06 is fine for 3 gpm, but getting iffy for 6 gpm. But the block is a local restriction -- in and of itself, it forms a small part of the entire system. The restriction in any elbows is several times greater.
But my thought was actually more related to fitting and hose sizes. If the hydraulic block port is the same size as the spool valve port, it simplifies the need for adapters.
OTOH, I like the idea of using 0-ring fittings over pipe threads. But the tooling costs are higher. If you already have the reamer and tap set for -08 then it's not an issue. If you only have -06 size available, then it adds to the cost for a small batch of orders. I threaded mine 3/4" pipe for two reasons: 1. adapters for a range of smaller hose sizes are readily available and 2. I already have 3/4" pipe taps. ;-)
I despise NPT threads and I have -04, -05, -06, -08, -10, and -12 port cutters so I can do just about anything in the CUT and small utility tractor hydraulics world. You need port adapters regardless of size or type so SAE-06 to SAE-08 is trivial. The downside is you will have obstructions and have to resort to long drop elbows. Personally I prefer -06 end fittings on -06 hose because it is a lot more compact than -08 and has exactly the same size stem. I also make hoses and I can put a wide variety of ends and sizes on them. Iif you want to get fancy something like this on the block end would be compact, easy to install, and look very "professional". Same cost as a short drop female JIC swivel and a port adapter.