Some people say for TCP, smaller packets give better acknowledgement pacing. ISCSI is kinda over local, single switch links for me, but general purpose TCP streamed data it may well be "smaller is better" for rate estimates and window management
Less packets to process would speed things up. Fever headers to process.
Also if your TCP flow bandwidth is counted in tens or hundreds of gigabits per second, there's still going to be plenty of ACKs.
Advertised MSS, interface MTU, and route MTU can all constrain packet sizing.
Using large-MTU routes for internal destinations can work well.